#include <bits/stdc++.h>
using namespace std;
inline int read() {
  long long res = 0;
  char ch = getchar();
  while (!isdigit(ch)) ch = getchar();
  while (isdigit(ch)) res = (res << 3) + (res << 1) + ch - '0', ch = getchar();
  return res;
}
void print(int x) {
  if (x < 0) putchar('-'), x = -x;
  if (x < 10)
    putchar(x + '0');
  else {
    print(x / 10);
    putchar(x % 10 + '0');
  }
}
void out(int a) {
  print(a / 10);
  print(a % 10);
}
int main() {
  int a, b, c, d;
  a = read();
  b = read();
  c = read();
  d = read();
  int l = a * 60 + b, r = c * 60 + d;
  if (l < r) l += 1440;
  l -= r;
  out(l / 60);
  printf(":");
  out(l % 60);
}
