#include <iostream>
using namespace std;
int main()
{
    long long s,v;
    int m,h,t;
    cin>>s>>v;
    t = double(s)/v+10;
    if (double(s)/v+10 - t >0) t+=1;
    if (t>480)
    {
        t -= 480;
        t = 1440 -480-t;
        h = t/60+8;
        m = t%60;
        cout<<(h>10 ? "":"0")<<h<<':'<<(m>=10 ? "":"0")<<m;

    }
    else if (t<480)
    {
        t = 480-t;
        h = t/60;
        m = t%60;
        cout<<'0'<<h<<':'<<(m>=10 ? "":"0")<<m;
    }
    if (-t+1440==480) cout<<"00:00";
    return 0;
}

以上是代码，恳请各位大牛斧正，以解心头之惑。