C++ :

#include <cstdio>
int main(){
    int h1, m1, h2, m2;
    if(scanf("%d:%d", &h1, &m1) != 2) return 0;
    if(scanf("%d:%d", &h2, &m2) != 2) return 0;
    int cur = h1 * 60 + m1;
    int dur = h2 * 60 + m2;
    int p = ((cur - dur) % 1440 + 1440) % 1440;
    printf("%02d:%02d\n", p / 60, p % 60);
    return 0;
}