N, K = gets.split.map(&:to_i)
Q = N.times.map { gets.split.map(&:to_i) }

def f(x)
  rank = 0

  Q.each do |a, b|
    if b < x
      rank += (b - a + 1)
    else
      rank += (x - a + 1)
    end
  end

  K <= rank
end

ok = 10 ** 9
ng = 0

while (ok - ng).abs >= 2
  x = (ok + ng) / 2

  if f(x)
    ok = x
  else
    ng = x
  end
end

puts ok