#include <bits/stdc++.h>
using namespace std;
int main() {
  char w[6], t[6];
  int h, m, th, tm;
  scanf("%s", w);
  scanf("%s", t);
  h = 10 * (int)w[0] + (int)w[1];
  m = 10 * (int)w[3] + (int)w[4];
  th = 10 * (int)t[0] + (int)t[1];
  tm = 10 * (int)t[3] + (int)t[4];
  m = m - tm;
  if ((h < th) || ((h == th) && (m > tm))) {
    h += 24;
  }
  h -= th;
  if (m < 0) {
    if (h == 0) {
      h = 23;
    } else {
      h--;
    }
    m += 60;
  }
  cout << setw(2) << std::setfill('0') << h << ":" << setw(2)
       << std::setfill('0') << m;
  return 0;
}
