#include <bits/stdc++.h>
using namespace std;
int main() {
  int h1, h2, m1, m2;
  char c[0];
  cin >> h1 >> c[0] >> m1;
  cin >> h2 >> c[0] >> m2;
  int hp = h1 - h2;
  int mp = m1 - m2;
  if (mp < 0) {
    mp += 60;
    hp -= 1;
  }
  if (hp < 0) hp += 24;
  printf("%02d:%02d", hp, mp);
  return 0;
}
