#include <bits/stdc++.h>
#define debug(x) cerr << #x << " " << x << "\n"
#define debugs(x) cerr << #x << " " << x << " "
#pragma GCC optimize("Ofast")
using namespace std;
typedef long long ll;
typedef pair <ll, ll> pii;
const ll NMAX = 5002;
const ll INF = (1LL << 60);
const ll nrbits = 20;
const int MOD = 998244353;
const int bucket = 320;
int mici[NMAX][NMAX];
int v[NMAX];
int dp[NMAX];
int st[NMAX][NMAX];
int main() {
#ifdef HOME
ifstream cin(".in");
ofstream cout(".out");
#endif // HOME
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int n, i;
cin >> n;
for(i = 1; i <= n; i++){
cin >> v[i];
}
for(i = 1; i <= n; i++){
for(int j = i + 1; j <= n; j++){
mici[v[i]][v[j]]++;
}
for(int j = 1; j <= i; j++){
st[v[i]][v[j]]++;
}
for(int j = 1; j <= n; j++){
st[v[i]][j] += st[v[i]][j - 1];
mici[v[i]][j] += mici[v[i]][j - 1];
}
}
for(int i = n; i >= 1; i--) dp[i] = 1e9;
for(int i = n; i >= 1; i--){
int sum = 0;
for(int j = i; j <= n; j++){
int nou = j;
sum += (mici[nou][i - 1] + st[nou][nou - 1] - st[nou][i - 1]);
dp[i] = min(dp[i], dp[j + 1] + sum);
}
}
cout << dp[1];
return 0;
}
