#include <bits/stdc++.h>
using namespace std;
int main() {
  int cHr, cMn, dHr, dMn, hr, mn;
  scanf("%d:%d", &cHr, &cMn);
  scanf("%d:%d", &dHr, &dMn);
  hr = cHr - dHr;
  if (hr < 0) hr = 24 + hr;
  mn = cMn - dMn;
  if (mn < 0) {
    hr--;
    if (hr < 0) hr = 24 + hr;
    mn = 60 + mn;
  }
  if (hr < 10)
    cout << "0" << hr << ":";
  else
    cout << hr << ":";
  if (mn < 10)
    cout << "0" << mn << endl;
  else
    cout << mn << endl;
  return 0;
}
