#include <iostream>
#include <cmath>
#include <iomanip>

int main() {
    double sum = 0, square_sum = 0, now, amount = 0;
    while (true) {
        std::cin >> now;
        if (now == 0) {
            break;
        }
        ++amount;
        sum += now;
        square_sum += now * now;
    }
    std::cout << std::setprecision(12) << std::sqrt((square_sum - sum * sum / amount) / (amount - 1));
}