#include<bits/stdc++.h>

#define ll long long

using namespace std;

const int maxn=;

const ll inf=1e18+;

int n,a[maxn],b[maxn];

ll f[maxn][maxn],mn[maxn];

inline ll min(ll a,ll b){return a<b?a:b;}

inline ll abs(ll a){return a<?-a:a;}

int main(){

    scanf("%d",&n);

    for(int i=;i<=n;i++)scanf("%d",&a[i]),a[i]-=i,b[i]=a[i];

    sort(b+,b++n);

    int bb=unique(b+,b++n)-b-;

    for(int i=;i<=n;i++){

        ll mn=inf;

        for(int j=;j<=bb;j++){

            mn=min(mn,f[i-][j]);

            f[i][j]=abs(b[j]-a[i])+mn;

        }

    }

    ll ans=inf;

    for(int i=;i<=bb;i++)

    ans=min(ans,f[n][i]);

    printf("%lld\n",ans);

}