27分，求调，玄关。

#include <bits/stdc++.h>
using namespace std;

/*你已经入以及战备状态，加油WePHe*/
int main() {
	long long x, y;
	cin >> x >> y;
	long long h = 7, m = 50;
	m -= 1;
	if (m - x / y <= 0) {
		if (h == 1) {
			h = 24;
		} else {
			h--;
		}
		m = (m - x / y) % 60;
	} else {
		m -= x / y;
	}
	if (h < 10) {
		cout << 0 << h << ':';
		if (m < 10) {
			cout << 0 << m << endl;
		} else {
			cout << m << endl;
		}
	} else {
		cout << h << m << endl;
	}

	return 0;
}