#include <bits/stdc++.h>
using namespace std;
int main() {
int n;
cin>>n;
vector<int> arr(n+1,0);
for(int i=1;i<=n;i++){
int element;
cin>>element;
arr[i]=element;
}
vector<int> dp(n+1, 0);
dp[1]=max(arr[1],0); //empty subset can be an answer
dp[2]=max(max(arr[1], arr[2]), 0);
for(int i=3;i<=n;i++){
dp[i]=max(dp[i-1], arr[i]+dp[i-2]);
}
cout<<dp[n];
return 0;
}
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