#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
class su{
public:
double gap;int gae;
bool operator < (const su &ss) const{
return gap < ss.gap;
}
};
int n;
int wichi[100001];
long long int res[100001];
long long int mn=-1;
su midd[100001];
long long int whole;
long long int mid1,mid2;
double mi1,mi2;
int lb1,ub1,lb2,ub2;
long long int calc(int obj){
long long int dap=0,gg=0;
for(int i=1;i<n;i++){
gg+=obj;
dap+=abs(gg-wichi[i]);
}
//printf("%d %lld\n",obj,dap);
return dap;
}
int main(){
long long int cnt=0;
scanf("%d",&n);
scanf("%d",&wichi[0]);
for(int i=1;i<n;i++){
scanf("%d",&wichi[i]);
midd[i-1].gap=wichi[i]/(double)i;
midd[i-1].gae=i;
}
whole=(n-1);
whole*=n;
whole/=2;
mid1=whole+1;mid1/=2;
mid2=mid1+((whole%2)==0);
sort(midd,midd+(n-1));
for(int i=0;i<n-1;i++){
// printf("%f %d\n",midd[i].gap,midd[i].gae);
if(cnt<mid1&&mid1<=cnt+midd[i].gae){
mi1=midd[i].gap;
}
if(cnt<mid2&&mid2<=cnt+midd[i].gae){
mi2=midd[i].gap;
break;
}
cnt+=midd[i].gae;
}
lb1=(int)mi1;ub1=lb1+1;
lb2=(int)mi2;ub2=lb2+1;
printf("%lld",min(calc(lb1),min(calc(ub1),min(calc(lb2),calc(ub2)))));
}
