红题40分？大佬求助！

#include<bits/stdc++.h>
using namespace std;
int main(){
	long long a,b,n,sum=0,day=0;
	cin>>a>>b>>n;
	while(sum<n){
		sum+=a*5+b*2;
		day+=7;
	}
	cout<<day;
	return 0;
}