Codeforces #551 Div2 A - Serval and Bus

cf551-div2-a.rb

n, t = gets.chomp.split(" ").map(&:to_i)
ret = 10**5
ans = -1
n.times do |i|
  s, d = gets.chomp.split(" ").map(&:to_i)
  while true
    if s >= t
      st = s - t
      if ret > st
        ret = st
        ans = i + 1
      end
      break
    end
    s += d
  end
end
puts ans