#include <bits/stdc++.h>
using namespace std;
template<typename T>
class Fenwick {
public:
int n;
vector<T> tree;
Fenwick(int n) : n(n), tree(n) {}
void Modify(int p, T x) {
for (int i = p; i < n; i |= i + 1) {
tree[i] += x;
}
}
T Query(int p) {
T res = 0;
for (int i = p; i > 0; i &= i - 1) {
res += tree[i - 1];
}
return res;
}
};
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int N;
cin >> N;
vector<int> H(N);
for (int i = 0; i < N; i++) {
cin >> H[i];
H[i]--;
}
// "sorted" = split H[0...N-1] into K segments,
// such that in each segment:
// H[i] == H[i + 1] + 1
// is satisfied.
vector<int> dp(N + 1, INT_MAX);
dp[0] = 0;
for (int i = 0; i < N; i++) {
vector<int> A;
vector<int> pos(N, -1);
for (int j = 0; j < N; j++) {
if (H[j] >= i) {
pos[H[j]] = A.size();
A.emplace_back(H[j]);
}
}
int sum_pos = 0;
int inversion = 0;
Fenwick<int> F(A.size());
for (int j = 1; i + j <= N; j++) { // segment = [i, i + j - 1]
F.Modify(pos[i + j - 1], 1);
sum_pos += pos[i + j - 1] - (j - 1); // place [i, i + j - 1] in front in any order
inversion += F.Query(pos[i + j - 1]) ; // sort [i, i + j - 1] in descending order
dp[i + j] = min(dp[i + j], dp[i] + sum_pos + inversion);
}
}
cout << dp[N] << '\n';
return 0;
}
