//
// Created by 曾仕邦 on 2021/7/19.
//

#include "bits/stdc++.h"
using namespace std;
bool cmp(long long a,long long b){
    return a>b;
}
int main(){
    int n;cin>>n;
    long long ans[1000100]={0};
    for (int i = 1; i <= n; ++i) {
        int temp; scanf("%d",&temp);
        ans[temp-i+500100] += temp;
    }
    long long res=0;
    sort(ans,ans+1000100,cmp);
    cout<<ans[0];
}