SDA - 2021-2022 - test5 - task 2

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <unordered_map>

using namespace std;


int main() {
    unordered_map<long long, int> counter;
    int n;
    long long num;

    cin >> n;

    for(int i = 0; i < n; i++){
        cin >> num;
        counter[num]++;
    }

    int sum = 0;
    for(auto i : counter){
        if(i.second % 2 == 1)
            sum += (i.second * i.first);
    }
    cout << sum;
    return 0;
}