#include <iostream>    
using namespace std;
int main()
{
    int s, v;
    cin >> s >> v;
    int i = s / v + 10;
    int t = 1920 - i - 1;\\神秘的手动向上取整
    if (t > 1440)
        t = t - 1440;
    int h = t / 60;
    int m = t % 60;
    if (h < 10)
        cout << "0" << h << ":";
    else
        cout << h << ":";
    if (m < 10)
        cout << "0" << m;
    else
        cout << m;
    return 0;
}

感觉题目要求都满足了，不知道为什么#9还是会wa，求解