#include<bits/stdc++.h>
using namespace std;
#ifndef BADGNU
#pragma GCC target("sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#endif
#pragma GCC optimize("Ofast,unroll-loops,fast-math,O3")
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define ll long long
#define int ll
#define ld long double
#define y1 cheza
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template<class T> using ordered_set = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
template<class T> using ordered_multiset = tree<T,null_type,less_equal<T>,rb_tree_tag,tree_order_statistics_node_update>;
const int N=305;
const int M=5001;
const int B=447;
const int mod=998244353;
const ll INF=1e18;
const int dx[]={1,-1,0,0};
const int dy[]={0,0,1,-1};
const double eps=1e-6;
int n;
int p[N];
int a[N];
int dp[2][N][N];
void test(){
cin>>n;
for(int i=1;i<=n;i++){
cin>>p[i];
}
for(int i=1;i<=n;i++){
for(int j=1;j<=n;j++){
dp[0][i][j]=(p[i]==j);
}
}
for(int k=1;k<=n-1;k++){
int ls=(k-1)%2;
int rs=k%2;
for(int i=1;i<=n-k;i++){
for(int j=1;j<=n-k;j++){
dp[rs][i][j]=0;
dp[rs][i][j]=max(dp[rs][i][j],dp[ls][i+1][j+1]+(p[i]==j));
dp[rs][i][j]=max(dp[rs][i][j],dp[ls][i+1][j]+(p[i]==j+k));
dp[rs][i][j]=max(dp[rs][i][j],dp[ls][i][j+1]+(p[i+k]==j));
dp[rs][i][j]=max(dp[rs][i][j],dp[ls][i][j]+(p[i+k]==j+k));
}
}
}
cout<<n-dp[(n-1)%2][1][1]<<'\n';
}
/*
*/
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
// cout.tie(nullptr);
int t2=1;
// cin>>t2;
for(int i=1;i<=t2;i++){
test();
}
}
