#include <stdio.h>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

int main(){
int n;
scanf("%d",&n);
vector<int> v(n);
for(int i=0;i<n;i++){
scanf("%d",&v[i]);
}
vector<int> dp(2);
for (int i = 0; i < n; i++){
	vector<int> dp2(2);
	dp2[0] = max(dp[0], dp[1]);
	dp2[1] = dp[0] + v[i];
	dp = dp2;
}
cout << max(dp[0], dp[1]) << endl;
return 0;
}