#include <iostream>
#include <bits/stdc++.h>
using namespace std;
 
int main() {
	// your code goes here
 
	int n;
	cin>> n;
 
	vector<int> arr(n+1,0);
 
	for(int i=1; i<=n; i++){
		cin>>arr[i];
	}
 
	vector<int> dp(n,0);
 
	dp[1] = arr[1];
	if(n==1) return arr[1];
 
	dp[2] = arr[2];
	if(n==2) return max(arr[1], arr[2]);
 
	dp[3] = arr[3] + arr[1];
	if(n==3)return max({arr[1], arr[2], arr[3], arr[1]+arr[3]});
 
	int i=4;
 
	while(i<=n){
 
		dp[i] = max(arr[i]+dp[i-2], dp[i-1]);
 
		i++;
	}
 
	cout<< dp[n];
 
	return 0;
}

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

NQoyIDQgNiA3IDg=

5
2 4 6 7 8