#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e7 + 5;
int l, r, x, y;
char c;
int main() {
  cin >> l >> c >> r;
  cin >> x >> c >> y;
  l = l * 60 + r;
  x = x * 60 + y;
  l = l - x;
  if (l < 0) {
    l += 24 * 60;
  }
  printf("%02d:%02d\n", l / 60, l % 60);
  return 0;
}
