#include<iostream>
#include<cstdio>
#include<math.h>

using namespace std;


int main()
{
	float sum=0.0;
	for(int i=0;i<12;i++){
		float d;
		cin>>d;
		sum += d;
	}
	
	sum = 1000*sum/12+5;
    sum = (int)(sum/10);
	sum = sum/100;
	printf("$%.2f\n",sum);
	
	return 0;
}