1
n, k = map(int, input().split())
2
ans = -10 ** 9
3
for i in range(n):
4
    f, t = map(int, input().split())
5
    if t <= k:
6
        ans = max(ans, f)
7
    else:
8
        ans = max(ans, f - (t - k))
9
print(ans)