// Wounds should become scars but I'm cracked instead U+1FAE0
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
#define all(x) (x).begin(),(x).end()
#define X first
#define Y second
#define sep ' '
#define endl '\n'
#define debug(x) cerr << #x << ": " << x << endl;
const ll MAXN = 300 + 10;
int dp[MAXN][MAXN][MAXN], n, A[MAXN];
int main() {
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin >> n;
for (int i = 1; i <= n; i++) cin >> A[i];
for (int len = 1; len <= n; len++) {
for (int l = 1; l <= n - len + 1; l++) {
for (int tl = 1; tl <= n - len + 1; tl++) {
int r = l + len - 1;
int tr = tl + len - 1;
if (A[l] == tl) dp[len][l][tl] = dp[len - 1][l + 1][tl + 1] + 1;
else if (A[r] == tl) dp[len][l][tl] = dp[len - 1][l][tl + 1] + 1;
else if (A[l] == tr) dp[len][l][tl] = dp[len - 1][l + 1][tl] + 1;
else if (A[r] == tr) dp[len][l][tl] = dp[len - 1][l][tl] + 1;
else dp[len][l][tl] = max({
dp[len - 1][l][tl],
dp[len - 1][l + 1][tl],
dp[len - 1][l][tl + 1],
dp[len - 1][l + 1][tl + 1]
});
}
}
}
cout << n - dp[n][1][1] << endl;
return 0;
}
