#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef double ld;
void debug_out(){cerr<<endl;}
template<typename Head, typename... Tail>
void debug_out(Head H, Tail... T){
cerr << H << ' ';
debug_out(T...);
}
#define debug(...) cerr << "(" << #__VA_ARGS__ << "): ", debug_out(__VA_ARGS__)
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define MP(x, y) make_pair(x, y)
const int maxn = 300 + 10;
int n, a[maxn];
int dp[maxn][maxn][maxn];
int main(){
cin >> n;
for (int i = 1; i <= n; i++){
cin >> a[i];
}
for (int i = n; i; i--){
for (int j = 1; j <= n; j++){
dp[i][i][j] = (a[j] != i);
}
for (int j = i+1; j <= n; j++){
for (int k = 1; k+j-i <= n; k++){
dp[i][j][k] = min({dp[i+1][j][k] + (a[k+j-i] != i), dp[i+1][j][k+1] + (a[k] != i)
, dp[i][j-1][k] + (a[k+j-i] != j), dp[i][j-1][k+1] + (a[k] != j)});
}
}
}
cout << dp[1][n][1] << '\n';
}
