两个样例过不了，求大佬解答（初学者见谅）

#include<bits/stdc++.h>
using namespace std;

int main(){
	double a,b;
	cin>>a>>b;
	int ans=10;
	ans+=ceil(a/b);
	int x,y=60;
	if(ans<=480) {
	x=8-ceil(double(ans)/60);
	cout<<0<<x<<":";
	y-=ans%60;
	if(y==60){
		y=0;
		cout<<y<<0;
	}else cout<<y;
	}
	else{
	ans=ans-480;
	y=60;
	x=24-ceil(double(ans)/60);
	cout<<x<<":";
	y=60-ans%60;
	if(y==60){
		y=0;
		cout<<y<<0;
	}else cout<<y;
	}
	return 0;
}