#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000

int main(){
	
	int n;
	cin>>n;
	
	vector<int> v(n);
	rep(i,n)cin>>v[i];
	
	
	vector<int> dp(2,0);
	
	rep(i,n){
		vector<int> ndp(2,0);
		rep(j,2)ndp[j] = max(ndp[j],dp[j]);
		ndp[0] = max(ndp[0],dp[1]);
		ndp[1] = max(ndp[1],dp[0]+v[i]);
		swap(dp,ndp);
	}
	cout<<max(dp[0],dp[1])<<endl;
	
	return 0;
}