n,k = gets.split.map(&:to_i)
a,b = 2.times.map{Array.new(n,0)}
n.times do |i|
    a[i],b[i] = gets.split.map(&:to_i)
end
min = 1
max = 10**15
while max-min > 1
    mid = (min+max)/2
    cnt = 0
    n.times do |i|
        if a[i] <= mid
            cnt += (b[i] < mid ? b[i] : mid)-a[i]+1
        end
    end
    if cnt < k
        min = mid
    else
        max = mid
    end
end
puts max