N,K = map(int,input().split())
AB = []
for i in range(N):
    AB.append(list(map(int,input().split())))

def is_ok(v):
    temp = 0
    for a,b in AB:
        temp+=max(0,min(v,b)-a+1)
    return temp>K


def meguru_bisect(ng, ok):
    while (abs(ok - ng) > 1):
        mid = (ok + ng) // 2
        if is_ok(mid):
            ok = mid
        else:
            ng = mid
    return ok

print(meguru_bisect(0,10**9+100))