#include<bits/stdc++.h>
using namespace std;
#define int long long
#define fi first
#define se second
#define pb push_back
#define debug(x) cout<<#x<<": "<<x<<"\n"
signed main()
{
ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
// freopen("input.000","r",stdin);
// freopen("output.000","w",stdout);
// srand((unsigned)time(NULL));
// rand()
int n,i,j,k,a[5005],dp[5005],b[5005],m,cost,pos;
cin>>n;
for (i=1;i<n+1;i++) cin>>a[i];
dp[n]=dp[n+1]=0;
for (i=n-1;i>0;i--)
{
dp[i]=1e12;
m=0;
for (j=1;j<n+1;j++) if (a[j]>=i)
{
m++;b[m]=a[j];
}
for (j=i+1;j<=n+1;j++)
{
cost=0;
for (k=i;k<j;k++)
{
pos=1;
while (b[pos]!=k)
{
if (b[pos]<k or b[pos]>=j) cost++;
// cout<<pos<<" "<<cost<<" "<<k<<" "<<j<<" "<<b[pos]<<"\n";
pos++;
}
}
dp[i]=min(dp[i], cost + dp[j]);
// cout<<i<<" "<<j<<" "<<cost+dp[j]<<"\n";
}
}
// for (i=1;i<n+1;i++) cout<<dp[i]<<" ";
cout<<dp[1];
}
