include[HTML_REMOVED]
include[HTML_REMOVED]
include[HTML_REMOVED]
using namespace std;
unordered_map [HTML_REMOVED] mp;
long long ret;
int main()
{ int n;
cin>>n;
for(int i=1;i<=n;i++)
{
int temp;
cin>>temp;
mp[temp-i]+=temp;
ret=max(mp[temp-i],ret);
}
cout<<ret<<endl;
return 0;
}