#include<bits/stdc++.h>
using namespace std;

void maimun()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
}

int main() {
    #ifdef ONLINE_JUDGE
        freopen("opertaionsJ.in", "r", stdin);
        freopen("operationsJ.out", "w", stdout);
    #endif
    maimun();

    int n;
    cin >> n;

    int freq[103] = {};
    for (int i = 0; i < n; ++i) {
        int x;
        cin >> x;
        freq[abs(x)]++;
    }

    int total = 0;
    int remaining = n;

    for (int i = 1; i <= 102; ++i) {
        if (freq[i] > 0) {
            total += i;
            remaining -= freq[i];
        }
    }

    cout << total << endl;
    return 0;
}