#define _CRT_SECURE_NO_WARNINGS
#include <math.h>
#include<iostream>
#include<cstdio>
#include<algorithm>
#include<string>
using namespace std;
double q;
int main() {
    int  k,sum=0, i;
    double adv,c=0;
    cin >> k;
    for (i = 1; i <= k; i++)
    {
        cin >> q;
        if (q>=15  &&q<= 25) 
            c += q;
        else break;
    }
    adv = c / k;
    printf("%.2f\n", adv);
   /* cout << adv<< endl;*/
    return 0;
}