n, k = map(int, input().split())
info = [list(map(int, input().split())) for i in range(n)]

def solve(mid):
    ans = 0
    for i in range(n):
        if info[i][0] < mid:
            ans += (min(mid, info[i][1]+1) - info[i][0])
    if ans < k:
        return True
    else:
        return False

ok = 0
ng = 10**9 + 1
while abs(ok - ng) > 1:
    mid = (ok + ng) // 2
    if solve(mid):
        ok = mid
    else:
        ng = mid
print(ok)