#include <bits/stdc++.h>
int main() {
  int a, b;
  scanf("%d:%d", &a, &b);
  int c, d;
  scanf("%d:%d", &c, &d);
  int ans1, ans2;
  if (b >= d)
    ans2 = b - d;
  else {
    ans2 = b + 60 - d;
    a--;
  }
  if (a >= c)
    ans1 = a - c;
  else {
    ans1 = a + 24 - c;
  }
  printf("%02d:%02d\n", ans1, ans2);
  return 0;
}
