#include <bits/stdc++.h>
using namespace std;
 
int fun(vector<int>& arr , int n){
	vector<int>dp(n+1,INT_MIN);
	dp[1] = arr[1];
	for(int i=2;i<=n;i++){
		if(i-1>=1)dp[i] = max(dp[i] , arr[i] + dp[i-1]);
		if(i-3>=1)dp[i] = max(dp[i] , arr[i] + dp[i-3]);
		if(i-5>=1)dp[i] = max(dp[i] , arr[i] + dp[i-5]);
	}
	return dp[n];
}
 
int main() {
	int n;
	cin>>n;
	vector<int>arr(n+1);
	for(int i=1;i<=n;i++){
		cin>>arr[i];
	}
 
	cout<< fun(arr,n);
	return 0;
}

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8
5 8 3 100 -5 -5 5 10