#include<bits/stdc++.h>
using namespace std;
unsigned long long a,b,c,sum,tim; 
int main(){
	cin>>a>>b>>c;
	tim=a+b+c;
	sum=2*a+3*b+4*c;
	unsigned long long d=0;
    unsigned long long num=0;
	while(sum/tim<3||(sum/tim==3&&sum%tim<0.5)){
		d+=1;
		sum+=5;
		tim+=1;
	}
	cout<<d;
	

	return 0;
}