#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("sse4")
using namespace std;
template <class T>
bool ckmin(T& a, const T& b) {
  return b < a ? a = b, 1 : 0;
}
template <class T>
bool ckmax(T& a, const T& b) {
  return a < b ? a = b, 1 : 0;
}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const long double pii = 3.14159265359;
const int MOD = 1000000007;
const char nl = '\n';
const int MX = 200001;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int N;
  cin >> N;
  vector<int> v(N);
  for (auto& i : v) cin >> i;
  unordered_map<int, long long> m;
  for (int x = 0; x < (N); x++) {
    m[v[x] - x] += v[x];
  }
  long long ans = -1;
  for (auto& i : m) ckmax(ans, i.second);
  cout << ans << nl;
  return 0;
}
