#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  int sum = 0;
  for (int i = 0; i < n - 1; i += 2) {
    sum += (abs(a[i] - a[i + 1]));
  }
  cout << sum;
  return 0;
}
