Berland scientist notice long ago world depend Berland population due persistent research area scientist manage find Berland chronology start moment people come land consider happen year after Berland year start chronology population equal 13 people second year however trace population number follow year ultimately difficult task find di number people Berland year di12di2 di13di112di2 of course know people live Berland moment tell possibly year country population equal A that s ask determine also possible find year begin Berland chronology Lets suppose year a1a2ak then define resident country year apart a variant look example explanation