#include <iostream>

#include <cstdio>

#include <cstring>

#include <algorithm>

#include <cmath>

using namespace std;

#define lc t[x].l

#define rc t[x].r

typedef long long ll;

const int N=1e6+,INF=1e9;

inline int read(){

    char c=getchar();int x=,f=;

    while(c<''||c>''){if(c=='-')f=-; c=getchar();}

    while(c>=''&&c<=''){x=x*+c-''; c=getchar();}

    return x*f;

}

int n,a[N];

struct node{

    int l,r,v,d,size;

    node(){l=r=v=d=size=;}

}t[N];

int sz;

int Merge(int x,int y){

    if(x==||y==) return x|y;

    if(t[x].v<t[y].v) swap(x,y);

    rc=Merge(rc,y);

    t[x].size=t[lc].size+t[rc].size+;

    if(t[lc].d<t[rc].d) swap(lc,rc);

    t[x].d=t[rc].d+;

    return x;

}

inline int nw(int v){

    t[++sz].v=v;

    t[sz].size=;

    return sz;

}

inline int top(int x){return t[x].v;}

inline int size(int x){return t[x].size;}

inline void pop(int &x){x=Merge(lc,rc);}

ll ans;

int rt[N],p,l[N],r[N],tot[N];

void solve(){

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

        rt[++p]=nw(a[i]);

        l[p]=r[p]=i;tot[p]=;

        while(p-&&top(rt[p-])>top(rt[p])){

            rt[p-]=Merge(rt[p-],rt[p]);

            p--;

            r[p]=i;

            while(size(rt[p])>(r[p]-l[p]+)/) pop(rt[p]);

        }

    }

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

        for(int j=l[i];j<=r[i];j++) ans+=abs(a[j]-top(rt[i]));

    printf("%lld",ans);

}

int main(){

    //freopen("in.txt","r",stdin);

    n=read();

    for(int i=;i<=n;i++) a[i]=read()-i;

    t[].d=-;

    solve();

    return ;

}