#include <bits/stdc++.h>
#define El 2000000000
#define Dim 5001
using namespace std;
ifstream f("secv.in");
ofstream g("secv.out");
long Sir[Dim],n,maxim,Dist[Dim];

int main()
{
    f>>n;
    for(int i=1;i<=n;i++)
    {
        f>>Sir[i];
        maxim=max(maxim,Sir[i]);
        Dist[i]=5005;
    }
    for(long i=1;i<=maxim-1;i++)
        for(long l=1;l<=n;l++)
        for(long j=1;j<=n;j++)
        {
            if(Sir[j]==i&&Sir[j+l]==i+1)
            {
                if(l+Dist[j]>Dim-1)
                Dist[j+l]=min(Dist[j+l],l);
                else
                Dist[j+l]=min(Dist[j+l],l+Dist[j]);
            }
        }
    g<<Dist[n]+1;
    return 0;
}