naturalnum=gets.chomp.split(" ").map(&:to_i)
puts ((naturalnum[0]*2+naturalnum[1])%3==0&&(naturalnum[0]+naturalnum[1]*2)%3==0)? ((naturalnum[0]+naturalnum[1]*2)/3-(naturalnum[0]*2+naturalnum[1])/3)+1 : (naturalnum[0]+naturalnum[1]*2)/3-(naturalnum[0]*2+naturalnum[1])/3