#include <bits/stdc++.h>
using namespace std;
int main() {
  string a, b;
  cin >> a;
  getchar();
  cin >> b;
  int a1, a2, b1, b2, c1, c2;
  a1 = 10 * (a[0] - '0') + (a[1] - '0');
  a2 = 10 * (a[3] - '0') + (a[4] - '0');
  b1 = 10 * (b[0] - '0') + (b[1] - '0');
  b2 = 10 * (b[3] - '0') + (b[4] - '0');
  c1 = a1 - b1;
  c2 = a2 - b2;
  while (c2 < 0) {
    c2 += 60;
    c1 -= 1;
  }
  while (c1 < 0) {
    c1 += 24;
  }
  printf("%02d:%02d", c1, c2);
  return 0;
}
