JOHANNESBURG, SOUTH AFRICA – DECEMBER 10: U.S. President Barack Obama (L) shakes hands with Cuban President Raul Castro during the official memorial service for former South African President Nelson Mandela at FNB Stadium December 10, 2013 in Johannesburg, South Africa. Over 60 heads of state have travelled to South Africa to attend a week of events commemorating the life of former South African President Nelson Mandela. Mr Mandela passed away on the evening of December 5, 2013 at his home in Houghton at the age of 95. Mandela became South Africa’s first black president in 1994 after spending 27 years in jail for his activism against apartheid in a racially-divided South Africa. (Photo by Chip Somodevilla/Getty Images)