#include <iostream>
#include <vector>
#include <cmath>
#include <string>
#include <fstream>
#include <cstdlib>

inline double to_2(double x)
{
    return x * x;
}

class InsuficientDataException {

};

double stdev(std::vector<double> const &v)
{
    size_t N = v.size();

    if (N < 2) {
        throw InsuficientDataException();
    }

    double s{0};
    for (auto &x: v) {
        s += x;
    }

    double m{s / N};

    s = 0;
    for (auto &x: v) {
        s += to_2(x - m);
    }

    return sqrt(s / (N - 1));
}

class FileException {

};

class FileNotFoundException : public FileException {

};

class FileReadException : public FileException {

};

double stdev_from_file(std::string filename)
{
    std::ifstream file(filename);
    if (! file.good()) {
        throw FileNotFoundException();
    }
    file.exceptions(std::ios::failbit | std::ios::badbit);

    std::vector<double> v;
    try {
        int N;
        file >> N;
        v.resize(N);
        for (int i = 0; i < N; ++i) {
            file >> v[i];
        }
    }
    catch (std::ifstream::failure e) {
        throw FileReadException();
    }
    return stdev(v);
}

int main(int argc, char *argv[])
{
    if (argc != 2) {
        std::cerr << "Usage: " << argv[0]
                  << " <filename>\n";
        exit(1);
    }

    double val;
    try {
        val = stdev_from_file(argv[1]);
        std::cout << "The standard deviation is " << val << std::endl;
    }
    catch (FileNotFoundException &e) {
        std::cerr << "The file " << argv[1] << " does't exist.\n";
        return 1;
    }
    catch (FileReadException &e) {
        std::cerr << "The file " << argv[1] << " is not in the expected format.\n";
        return 1;
    }
    catch (FileException &e) {
        // Esta poderia pegar as duas anteriores (experimente comentar).
        std::cerr << "Something wrong with the file " << argv[1] << std::endl;
    }
    catch (InsuficientDataException &e) {
        std::cerr << "Not enough values to compute standard deviation.\n";
    }

    return 0;
}