#include <bits/stdc++.h>
using namespace std;
int n, mmm, a[100000];
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= 2 * n; i++) {
    scanf("%d", &a[i]);
  }
  sort(a + 1, a + 1 + 2 * n);
  for (int i = 1; i <= 2 * n; i += 2) {
    mmm += min(a[i], a[i + 1]);
  }
  cout << mmm;
}
