#include <stdio.h>
#include <math.h>

int main(void){
	int n,i;
	int score[1000];
	int sum;
	double a,a2,m;
	
	while(1){
		scanf("%d",&n);
		if(n==0)
			break;
		sum=0;
		a=0;
		a2=0;
		m=0;
		for(i=0; i<n; i++){
			scanf("%d", &score[i]);
			sum += score[i];
		}
		m = (double)sum/n;
		for(i=0; i<n; i++){
			a2 += pow((score[i]-m),2);
		}
		a2 = a2/n;
		a = sqrt(a2);
		printf("%.8f\n",a);

	}

	return 0;
}