#include <bits/stdc++.h>   const int maxn = 4e5 + 10;   const int maxm = 2e5 + 10;   const int inf = 0x3f3f3f3f;   const long long mod = 1e9 + 7;   const double eps = 1e-7;   using namespace std;   long long cnt[25][25], dp[1 << 21];   int n;   vector<int> col[25];   int main() {     ios::sync_with_stdio(false);     cin.tie(0);     cout.tie(0);     cin >> n;     for (int i = 1; i <= n; i++) {       int x;       cin >> x;       col[x].push_back(i);     }     for (int i = 1; i <= 20; ++i)       for (int j = 1; j <= 20; ++j)         if (i != j) {           if (!col[i].size() || !col[j].size()) continue;           int l = 0;           for (int k = 0; k < col[i].size(); ++k) {             while (true) {               if (l == col[j].size() - 1 || col[j][l + 1] > col[i][k]) break;               l++;             }             if (col[j][l] < col[i][k]) cnt[i][j] += l + 1;           }         }     memset(dp, 0x3f, sizeof dp);     dp[0] = 0;     for (int S = 0; S < 1 << 20; ++S) {       for (int i = 0; i < 20; ++i)         if (!(S >> i & 1)) {           long long sum(0);           for (int j = 0; j < 20; ++j)             if (S >> j & 1) sum += cnt[j + 1][i + 1];           dp[S | (1 << i)] = min(dp[S | (1 << i)], dp[S] + sum);         }     }     cout << dp[(1 << 20) - 1] << endl;     return ~~(0 - 0);   }   