#include <bits/stdc++.h>
using namespace std;
int minu(string& s) {
  int hh = (s[0] - '0') * 10 + (s[1] - '0');
  int mm = (s[3] - '0') * 10 + (s[4] - '0');
  return hh * 60 + mm;
}
int main() {
  string s0, s1;
  cin >> s0 >> s1;
  int x = (24 * 60 + minu(s0) - minu(s1)) % (24 * 60);
  int hh = x / 60;
  int mm = x % 60;
  cout << (hh / 10) << (hh % 10) << ':';
  cout << (mm / 10) << (mm % 10) << endl;
  return 0;
}
