说实在，我按题解demo的过不了，换个思路，会简单

#include<bits/stdc++.h>
using namespace std;
int s,v,tT,dT;
int main(){
cin>>s>>v;
tT=ceil(s/(double)v)+10;
dT=8*60-tT;
if(dT<0){
    dT+=24*60;
}
int h=dT/60;
int m=dT%60;
cout<<(h<10?"0":"")<<h<<":"<<(m<10?"0":"")<<m<<endl;
return 0;
}