Him and me against the world

In a post apocalyptic world after a nuclear war the population grew until it the earth couldn't take it. The heads of state started to the culling. They killed off so many people so there were only a few thousand left. Then the program started. In order to sustain population growth every five years a boy and a girl would be chosen to breed. It was illegal for anyone else to breed. The chosen boy and girl would be kept in different c