看的是C171507的题解，看着思路打的，对了代码好几遍，没看出啥问题

代码如下

#include <bits/stdc++.h>
using namespace std;
int s,v;
long long cT,aT,bT,gH,gM;
int main()
{
    aT = 8 * 60 + 24 * 60;
    cin >> s >> v;
    if ( s%v != 0)
    {
        cT = ceil (s/v + 11);
    }
    else 
    {
        cT = s/v + 10;
    }
    aT = aT - cT;
    if (aT >= 24 * 60)
        aT = aT - 24 * 60;
    gH = aT / 60;
    gM = aT % 60;
    if (gM > 10)
    {
        if (gH > 10)
            cout << "0" << gH << ":0" << gM;
        else
            cout << "0" << gH << ":" << gM;
    }
    else 
    {
        if (gH < 10)
            cout << gH << ":0" << gM;
        else
            cout << gH << ":" << gM;
    }
    return 0;
}