#include <bits/stdc++.h>
int main() {
  int sh, sm, th, tm, ph, pm;
  scanf("%d:%d", &sh, &sm);
  scanf("%d:%d", &th, &tm);
  ph = sh - th;
  pm = sm - tm;
  if (pm < 0) {
    pm += 60;
    ph -= 1;
  }
  if (ph < 0) ph += 24;
  printf("%02d:%02d\n", ph, pm);
  return 0;
}
