#include <bits/stdc++.h>
using namespace std;
int main() {
  int t1h, t1m, dth, dtm;
  scanf("%d:%d%d:%d", &t1h, &t1m, &dth, &dtm);
  int t1 = t1h * 60 + t1m;
  int dt = dth * 60 + dtm;
  int t0 = (t1 - dt + 1440) % 1440;
  printf("%02d:%02d\n", t0 / 60, t0 % 60);
}
