#include <bits/stdc++.h>   using namespace std;   int main() {     int n;     cin >> n;     int b;     map<int, long long> mp;     long long a = -1;     if (n > 1) {       for (int i = 0; i < n; i++) {         cin >> b;         mp[b - i] += b;         a = max(a, mp[b - i]);       }       cout << a;     } else {       cin >> b;       cout << b;     }   }   