N,K = map(int,input().split())
lsAB = []
for i in range(N):
    A,B = map(int,input().split())
    lsAB.append((A,B))

def is_ok(arg):
    cnt = 0
    for i in range(N):
        cnt += max(0,min(arg,lsAB[i][1])-lsAB[i][0]+1)
    return cnt >= 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**18+1))