#include <bits/stdc++.h>
using namespace std;
int realTime(char a, char b) {
  int ans = 0;
  ans += (int)a - 48;
  ans *= 10;
  return ans + (int)b - 48;
}
int main() {
  string s;
  cin >> s;
  string t;
  cin >> t;
  if (t[0] == '0' && t[1] == '0' && t[3] == '0' && t[4] == '0') {
    cout << s;
    return 0;
  }
  int h1 = realTime(s[0], s[1]);
  int m1 = realTime(s[3], s[4]);
  int h2 = realTime(t[0], t[1]);
  int m2 = realTime(t[3], t[4]);
  h1 -= h2;
  if (h1 < 0) h1 += 24;
  m1 -= m2;
  if (m1 < 0) {
    m1 += 60;
    h1--;
    if (h1 < 0) h1 = 23;
  }
  if (h1 < 10)
    cout << 0 << h1 << ":";
  else
    cout << h1 << ":";
  if (m1 < 10)
    cout << 0 << m1;
  else
    cout << m1;
  return 0;
}
