#include <iostream>
#include <vector>
#include <cstdlib>
 
struct vector_t: public std::vector<int> {
	int&  operator [] (unsigned int i){
		if( this->size() <= i ){ this->resize(i+1); }
		return this->at(i);
	}
};
 
 
int main(){
	using namespace std;
    vector_t t;
    int cnt, ten, i;
    double sum, avg;
 
	cnt = 0;
	cin >> ten;
 
	label_1:
    if( ten != 999 ){
        t[cnt] = ten;
        cnt = cnt + 1;
	    cin >> ten;
		goto label_1;
    }
	sum = 0;
	i = 0;
 
	label_2:
	if( i < cnt ){
		sum = sum + t[i];
		i = i + 1;
		goto label_2;
	}
	avg = sum / cnt;
 
	cout << avg << endl;
 
	exit(0);
}