#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define fi first
#define se second
#define vi vector<int>
#define vll vector<long long>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
mt19937_64 rng64(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int rand(int l,int r){return uniform_int_distribution<int>(l, r)(rng);}
inline ll rand(ll l,ll r){return uniform_int_distribution<ll>(l, r)(rng64);}
#ifdef DEBUG
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif
struct custom_hash {
static uint64_t splitmix64(uint64_t x) {
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const {
static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
return splitmix64(x + FIXED_RANDOM);
}
};
struct pair_hash{
size_t operator()(const pair<int,int>&x)const{
return hash<long long>()(((long long)x.first)^(((long long)x.second)<<32));
}
};
const int MAXN = 5e3 + 7;
const int INF = 1e9;
ll dp[MAXN];
int pre[MAXN][MAXN];
int post[MAXN][MAXN];
int Pos[MAXN];
int A[MAXN];
int n;
//ile jest na prawo, takich które będą przechodzić na lewo
int countOnRight(int x, int pr){
int p = Pos[x];
return post[p][n] - (post[p][x] - post[p][pr]);
}
void solve(){
cin >> n;
for(int i = 1; i <= n; i++){
cin >> A[i];
Pos[A[i]] = i;
}
for(int i = n; i >= 1; i--){
dp[i] = INF;
for(int j = 1; j <= n; j++){
post[i][j] = post[i + 1][j];
if(j >= A[i]){
post[i][j]++;
}
}
}
dp[0] = 0;
for(int i = 0; i < n; i++){
//policzyłeś dla i
ll curr = dp[i];
for(int j = n; j > i; j--){
curr = (ll)curr + countOnRight(j, i);
}
dp[n] = min(dp[n], curr);
for(int j = n; j > i + 1; j--){
//z aktualnego rozw. usuwasz j
curr = (ll)curr - countOnRight(j, i);
dp[j - 1] = min(dp[j - 1], curr);
}
}
// for(int i = n; i >= 1; i--){
// cout << i << ' ' << dp[i] << '\n';
// }
cout << dp[n] << '\n';
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);
cout.tie(NULL);
int t = 1;
//cin >> t;
while(t--){
solve();
}
return 0;
}
