#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int calc(int n, vector<int>& a, vector<int> b) {
int res = 0;
for (int i = 0; i < n; ++i) {
int id = -1;
for (int j = i; j < n; ++j) {
if (b[j] == a[i]) {
id = j;
break;
}
}
while (id > i) {
swap(b[id - 1], b[id]);
id -= 1;
res += 1;
}
}
assert(b == a);
return res;
}
bool ok(int n, vector<int> a) {
int mx = 0;
for (int i = 0; i < n; ++i) {
if (2 * i + a[i] <= mx) {
return false;
}
mx = max(mx, 2 * i + a[i]);
}
return true;
}
int main() {
int n;
cin >> n;
vector<int> tmp(n);
iota(begin(tmp), end(tmp), 1);
vector<int> b(n);
for (auto& u : b) cin >> u;
//~ int res = n * n;
//~ cout << ok(9, {1, 9, 8, 7, 6, 5, 4, 3, 2}) << "\n";
vector<vector<vector<int>>> dp(n + 1, vector<vector<int>>(n, vector<int>(n, -1)));
auto dfs = [&](auto& dfs, int i, int j, int num, vector<int> a) -> int {
if (i > n) {
//~ cerr << "Ended:\n";
//~ for (auto& u : a) {
//~ cerr << u << " ";
//~ }
//~ cerr << "\n";
assert(ok(n, a));
return 0;
}
if (dp[i][j][num] != -1) {
//~ cerr << "Memo!\n";
return dp[i][j][num];
}
int nres = n * n;
for (int k = j; k < n; ++k) {
auto na = a;
int now = 0;
for (int l = j; l <= k; ++l) {
int id = -1;
int need = i + (k - l);
//~ cerr << i << " " << j << " = " << need << "\n";
//~ for (auto& u : na) {
//~ cerr << u << " ";
//~ }
//~ cerr << "\n";
for (int l1 = l; l1 < n; ++l1) {
if (need == na[l1]) {
id = l1;
break;
}
}
assert(id != -1);
while (id > l) {
swap(na[id], na[id - 1]);
id -= 1;
now += 1;
}
}
now += dfs(dfs, i + k - j + 1, j + k - j + 1, num, na);
nres = min(nres, now);
//~ cerr << now << "\n";
//~ for (auto& u : na) {
//~ cout << u << " ";
//~ }
//~ cout << "\n";
//~ cerr << i << " " << k << " = " << now << "\n";
}
return dp[i][j][num] = nres;
};
cout << dfs(dfs, 1, 0, 0, b) << "\n";
//~ do {
//~ if (ok(n, a)) {
//~ res = min(res, calc(n, b, a));
//~ cout << calc(n, a, b) << " = ";
//~ if (calc(n, b, a) == 9) {
//~ for (auto& u : a) {
//~ cout << u << " ";
//~ }
//~ cout << "\n";
//~ }
//~ }
//~ } while (next_permutation(begin(a), end(a)));
//~ cout << res << "\n";
}
