#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;

#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(x) begin (x), end(x)
#define sz(x) (int) (x).size()
#define rep(i,a,b) for (int i = (a); i < (b); i++)

mt19937 rng(random_device{}());

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    int n;
    cin >> n;
    //int comb = n/2 * (n-1);
    vi a(n+1);
    rep(i,1,n+1) cin >> a[i];
    sort(a.begin(), a.end());
    int mexSum = 0;
    rep(i,1,n+1){
        rep(j,i+1,n+1){
            int k = 1;
            while(k == a[i] || k == a[j]){
                k++;
            }
            mexSum += k;
        }
    }
    cout << mexSum;
}