Combo photo taken on April 8, 2010 shows U.S. President Barack Obama (L) and his Russian counterpart Dmitry Medvedev reacts before (Up) and after signing a landmark nuclear arms reduction treaty in Prague, capital of Czech Republic. Under the new pact, the two countries agreed to reduce their deployed nuclear warheads to 1,550 each, or 30 percent below the current level of 2,200, and cut the launchers below 700 each.[Wu Wei/Xinhua]