U.S. President Barack Obama extends his hand to Russian President Vladimir Putin during their meeting at the United Nations General Assembly in New York September 28, 2015. REUTERS/Kevin Lamarque 

China's President Xi Jinping (R) shakes hands with Taiwan's President Ma Ying-jeou during a summit in Singapore November 7, 2015. REUTERS/Edgar Su TPX IMAGES OF THE DAY 

China's President Xi Jinping is welcomed by Britain's Prime Minister David Cameron at 10 Downing Street, in central London, Britain, October 21, 2015. REUTERS/Toby Melville 

Jeroen Dijsselbloem, (L) head of the euro zone finance ministers' group, and then Greek Finance Minister Yanis Varoufakis shake hands after their common press conference at the ministry in Athens January 30, 2015. Greece's government will not cooperate with the EU and IMF mission bankrolling the country and will not seek an extension to the bailout programme, its finance minister said at the conference. REUTERS/Kostas Tsironis 

Britain's Prince Charles (L) shakes hands with Gerry Adams at the National University of Ireland in Galway, Ireland May 19, 2015. Britain's Prince Charles met Gerry Adams in Ireland, the first time the leader of the former political wing of the Irish Republican Army (IRA) has met a senior member of the royal family, his Sinn Fein party said. REUTERS/Brian Lawless/pool 

India's Prime Minister Narendra Modi (L) shakes hands with his Pakistani counterpart Nawaz Sharif (2-R) in front of Nepal's Prime Minister Sushil Koirala (C) during the closing session of 18th South Asian Association for Regional Cooperation (SAARC) summit in Kathmandu November 27, 2014. REUTERS/Niranjan Shrestha/Pool 

China's President Xi Jinping (R) shakes hands with Japan's Prime Minister Shinzo Abe during their meeting at the Great Hall of the People, on the sidelines of the Asia Pacific Economic Cooperation (APEC) meetings, in Beijing, China November 10, 2014. Xi and Abe held formal talks, the first time since the two leaders took office, a breakthrough in ending a two-year row between Asia's biggest economies over history and territory. REUTERS/Kim Kyung-Hoon 

Russian President Vladimir Putin (L) shakes hands with his Ukrainian counterpart Petro Poroshenko, as Kazakh President Nursultan Nazarbayev (C) stands nearby, in Minsk August 26, 2014. REUTERS/Sergei Bondarenko/Kazakh Presidential Office/Pool 

Russian President Vladimir Putin (2nd R), Crimea's Prime Minister Sergei Aksyonov (front L), Crimean parliamentary speaker Vladimir Konstantinov (back L) and Sevastopol Mayor Alexei Chaliy shake hands after a signing ceremony at the Kremlin in Moscow March 18, 2014. Putin and two Crimean leaders signed a treaty on making the Ukrainian Black Sea peninsula a part of Russia. REUTERS/Sergei Ilnitsky/Pool 

U.S. President Barack Obama (L) shakes hands with Saudi Arabia's King Salman at the start of a bilateral meeting at Erga Palace in Riyadh January 27, 2015. Obama sought to cement ties with Saudi Arabia as he came to pay his respects after the death of King Abdullah, a trip that underscored the importance of a U.S.-Saudi alliance that extends beyond oil interests to regional security. REUTERS/Jim Bourg 

Britain's Queen Elizabeth shakes hands with Northern Ireland deputy first minister Martin McGuinness, watched by first minister Peter Robinson (C) at the Lyric Theatre in Belfast June 27, 2012. Queen Elizabeth shook the hand of former Irish Republican Army (IRA) commander McGuinness for the first time, drawing a line under a conflict that cost the lives of thousands of soldiers and civilians, including that of her cousin. REUTERS/Paul Faith/pool 

U.S. Secretary of State Hillary Clinton (C) looks on as Israel's Prime Minister Benjamin Netanyahu (L) and President of the Palestinian Authority Mahmoud Abbas shake hands during direct talks aimed at peace in the Middle East, at the State Department in Washington, September 2, 2010. REUTERS/Jason Reed 

The late Venezuelan President Hugo Chavez (R) gives U.S. President Barack Obama a copy of "Las Venas Abiertas de America Latina" by author Eduardo Galeano during a meeting at the Summit of the Americas in Port of Spain, Trinidad April 18, 2009. REUTERS/Kevin Lamarque 

Zimbabwe's President Robert Mugabe (L) shakes hands with Morgan Tsvangirai (R), leader of Zimbabwe's main opposition Movement for Democratic Change (MDC), in Harare, Zimbabwe July 21, 2008. REUTERS/Philimon Bulawayo 

Former South African President F.W. de Klerk (L) and the late African National Congress (ANC) Deputy-President Nelson Mandela, agreed after 15 hours of talks on August 7, 1990 to suspend its armed struggle against white rule in South Africa. Reuters/Juda Ngwenya 

Republican Henry Hyde, then chairman of the U.S. House of Representatives'International Relations Committee (R), views an exhibition in Shanghai December 11, 2002. The
photograph shows the late Chinese Chairman Mao Zedong meeting then U.S. President Nixon on his historic visit to China in 1972. REUTERS/Claro Cortes IV 

Then U.S. President Ronald Reagan (R) shakes hands at his first meeting with then Soviet leader Mikhail Gorbachev to sign an arms treaty in Geneva, Switzerland in November 19, 1985. REUTERS/Denis Paquin