#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
#define ll long long
const int N = 5e3 + 5;
int dp[N];
int cnt[N][N], pd[N][N], sum[N][N];
int a[N], b[N], mx[N][N];
int main(){
int n; cin >> n;
for (int i = 1; i <= n; i++) cin >> a[i];
for (int i = 1; i <= n; i++) b[a[i]] = i;
for (int i = 1; i <= n; i++) {
mx[i][i] = b[i];
for (int j = i + 1; j <= n; j++) {
mx[i][j] = max(mx[i][j - 1], b[j]);
}
}
for (int i = 1; i <= n; i++) {
for (int j = 1; j < i; j++) {
cnt[a[i]][a[j]]++;
}
for (int j = n - 1; j > 0; j--) cnt[a[i]][j] += cnt[a[i]][j + 1];
}
for (int i = 1; i <= n; i++) {
for (int j = i + 1; j <= n; j++) {
pd[i][j] = pd[i][j - 1] + (cnt[j][i] - cnt[j][j]);
}
}
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= n; j++) {
cnt[i][j] += cnt[i - 1][j];
}
}
for (int i = 1; i <= n; i++) {
dp[i] = 1e9;
for (int j = 0; j < i; j++) {
int res = dp[j];
// for (int k = j + 1; k <= i; k++) {
// res += cnt[k][i + 1];
// }
res += cnt[i][i + 1] - cnt[j][i + 1];
res += pd[j + 1][i];
dp[i] = min(dp[i], res);
}
}
cout << dp[n];
}
