#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <iomanip>
using namespace std;

int main() {
    int N;
    cin >> N;

    vector<long double> A(N);
    for (int i = 0; i < N; i++) {
        cin >> A[i];
    }
    sort(A.begin(), A.end(), [](long double& a, long double& b) { return abs(a) < abs(b); });
    long double ans = 0;
    for (int i = 0; i < N; i++) {
        ans += A[i];
    }

    cout << fixed << setprecision(10) << ans << endl;
    
    return 0;
}