#include <iostream>

using namespace std;

int main()
{

  float sum;
  float n;

  while (1) {

    float x;
    cin >> x;

    //cout << x << endl;

    if (x==-1) break;

    sum += x;
    n   += 1.;

  }

  cout << "mean = " << (sum/n) << endl;

}