#include <bits/stdc++.h>
using namespace std;

using ll=long long;
ll mod=1000000007;
ll INF=1LL<<60;

int main() {
	int N;
	cin >> N;
	vector<int> V(N);
	for(int i=0;i<N;i++){
		cin >> V[i];
	}
	vector<vector<int>> dp(N+1,vector<int>(2));
	for(int i=0;i<N;i++){
		dp[i+1][0]=max(dp[i][0],dp[i][1]);
		dp[i+1][1]=dp[i][0]+V[i];
	}
	cout << max(dp[N][0],dp[N][1]) << endl;
}