#include <cstdio>
#include <cstring>
#include <iostream>
using namespace std;
const int maxn=1000010;
int v[maxn];
int l[maxn],r[maxn],rt[maxn],nvl[maxn],ch[maxn][2];
int n,m;
int merge(int x,int y)
{
	if(!x)	return y;
	if(!y)	return x;
	if(v[x]<v[y])	swap(x,y);
	ch[x][1]=merge(ch[x][1],y);
	if(nvl[ch[x][0]]<nvl[ch[x][1]])	swap(ch[x][0],ch[x][1]);
	nvl[x]=nvl[ch[x][1]]+1;
	return x;
}
long long ans;
long long z(int a)
{
	return (long long)(a>0?a:-a);
}
int main()
{
	scanf("%d",&n);
	int i,j;
	for(i=1;i<=n;i++)	scanf("%d",&v[i]),v[i]-=i;
	for(i=1;i<=n;i++)
	{
		l[++m]=r[m]=rt[m]=i;
		while(v[rt[m]]<v[rt[m-1]]&&m>1)
		{
			rt[m-1]=merge(rt[m-1],rt[m]);
			for(j=1;j<=(r[m-1]-l[m-1]+1)/2+1+(r[m]-l[m]+1)/2+1-(r[m]-l[m-1]+1)/2-1;j++)	rt[m-1]=merge(ch[rt[m-1]][0],ch[rt[m-1]][1]);
			r[m-1]=r[m],m--;
		}
	}
	for(i=1;i<=m;i++)
		for(j=l[i];j<=r[i];j++)
			ans+=z(v[rt[i]]-v[j]);
	printf("%lld",ans);
	return 0;
}