#include <bits/stdc++.h>
using namespace std;
int main() {
  int m1, m2, s1, s2;
  scanf("%d:%d", &m1, &s1);
  scanf("%d:%d", &m2, &s2);
  int m;
  m1 = m1 * 60 + s1;
  m2 = m2 * 60 + s2;
  m = m1 - m2;
  if (m < 0) m += 24 * 60;
  printf("%02d:%02d\n", m / 60, m % 60);
}
