#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
#include <queue>
#include <map>
#include <cmath>
#include <iomanip>

using namespace std;

int main() {
  int n;
  cin >> n;
  map<int,int> mp;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    mp[x]++;
  }
  int ans = 0;
  for (auto i : mp) {
    int pre = i.first - 1;
    if (mp[pre] == 0) {
      ans += i.first;
    }
  }
  cout << ans << endl;
  return 0;
}