传送门

#include<bits/stdc++.h>
using namespace std;
int main(){
	double s,v,t;
	int x=470,y,z;
	cin>>s>>v;
	t=ceil(s/v); 
	x-=t;
	if(t>x){
		x+=1440;
	}
	y=x/60;
	z=x%60;
	if(y<10){
		if(z<10)
			cout<<0<<y<<":"<<0<<z;
		else
			cout<<0<<y<<":"<<z;
	}else{
		 if(z<10)
			cout<<y<<":"<<0<<z;
		else
			cout<<y<<":"<<z;
	}
	return 0;
}