#include<bits/stdc++.h>
using namespace std;
unsigned long long int a,b,c,sum;
int main(){
	cin>>a>>b>>c;
	sum=a*2+b*3+c*4;
	unsigned long long int l=-1,r=10000000;
	while(l+1<r)
	{
		int mid=(l+r)/2;
		if(double(double(sum+mid*5)/double(a+b+c+mid))>=3.5) r=mid;
		else l=mid;
	}
	cout<<r;
	return 0;
}