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

def ok(x):
    ret = 0
    for a, b in ab:
        if x < a:
            continue
        else:
            ret += min(b, x) - a + 1
            if ret >= k:
                return True
    return False

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