#include <bits/stdc++.h>
int main() {
  int x1, x2, x3, x4;
  scanf("%d:%d%d:%d", &x1, &x2, &x3, &x4);
  if (x2 < x4) {
    x2 = x2 + 60 - x4;
    x3++;
  } else
    x2 = x2 - x4;
  if (x1 < x3)
    x1 = x1 + 24 - x3;
  else
    x1 = x1 - x3;
  printf("%02d:%02d\n", x1, x2);
}
