#include <bits/stdc++.h>
using namespace std;
int main() {
  char s[10];
  char t[10];
  cin >> s >> t;
  int ss =
      (s[0] - '0') * 600 + (s[1] - '0') * 60 + (s[3] - '0') * 10 + (s[4] - '0');
  int tt =
      (t[0] - '0') * 600 + (t[1] - '0') * 60 + (t[3] - '0') * 10 + (t[4] - '0');
  int ans = ss - tt;
  if (ans < 0) ans = ans + 24 * 60;
  int hour, min;
  hour = ans / 60;
  min = ans % 60;
  printf("%02d:%02d\n", hour, min);
  return 0;
}
