#include<iostream>
#include<cmath>
#include<iomanip>
using namespace std;
int main(){
  int n;
  while(cin>>n){
    if(n==0) break;
    double s[n],a = 0;
    double m = 0;
    for(int i=0;i<n;i++){
      cin >> s[i];
      m += s[i];
    }
    m /= n;
    for(int i=0;i<n;i++) a = a + (s[i]-m) * (s[i]-m);
    a /= n;
    cout << fixed << setprecision(5) << sqrt(a) << endl;
  }
  return 0;
}