#include <cstdio>
#include <cmath>
using namespace std;

int main(void){
    while(true){
        int n;
        double sum = 0, sum2 = 0 ;
        scanf("%d", &n);
        if(n == 0) break;
        for(int i = 0; i < n; i++){
            int x;
            scanf("%d", &x);
            sum += x;
            sum2 += x * x;
        }
        printf("%lf\n", sqrt((sum2 - sum * sum / n) / n));
    }

    return 0;
}


