#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=1e5+100;
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 ans=0;
void dfs(int l,int r,int lx,int rx){
if(l>r){
int res=0;
for(int i=1;i<=n;i++){
if(p[i]!=a[i]){
res++;
}
}
ans=min(ans,res);
return;
}
a[l]=lx;
dfs(l+1,r,lx+1,rx);
a[l]=rx;
dfs(l+1,r,lx,rx-1);
a[r]=lx;
dfs(l,r-1,lx+1,rx);
a[r]=rx;
dfs(l,r-1,lx,rx-1);
}
void test(){
cin>>n;
for(int i=1;i<=n;i++){
cin>>p[i];
}
ans=n;
dfs(1,n,1,n);
cout<<ans<<'\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();
}
}
