#include<cstdio>
#include<iostream>
#include<cmath>
#include<string>
#include<cstring>
#include<algorithm>
using namespace std;
int main(){
	double s,v;
	int t2,t3,ans1,ans2;
	cin>>s>>v;
	int t=ceil(s/v)+10;
	int t1=480-t;
	if(t1<0){
		t1=abs(t1);
		t2=t1/60;
		t3=t1%60;
		ans1=24-t2-1;
		ans2=60-t3;
	}
	else if(t1==0){
		cout<<"00:00";
		return 0;
	}
	else{
		t2=t1/60;
		t3=t1%60;
		ans1=8-t2-1;
		ans2=60-t3;
	}
	if(ans1<10)cout<<0<<ans1;
	else cout<<ans1;
	cout<<':';
	if(ans2<10)cout<<0<<ans2;
	else cout<<ans2;
    return 0;
}

代码见上 P5707