#include<iostream>
#include<algorithm>
#include<string>
#include<vector>
#include<iomanip>
#define RREP(i,s,e) for (i = s; i >= e; i--)
#define rrep(i,n) RREP(i,n,0)
#define REP(i,s,e) for (i = s; i < e; i++)
#define rep(i,n) REP(i,0,n)
#define INF 100000000
using namespace std;


int main(){
	int n;
	cin >> n;
	int v[n];

	int i;
	rep(i,n)
		cin >> v[i];

	int dp[1001][2];
	int j;
	


	dp[0][0] = 0;
	dp[0][1] = v[0];
	dp[1][0] = v[0];
	dp[1][1] = v[1];

	REP(i,2,n){
		dp[i][0] = max(dp[i-1][1],dp[i-2][1]);
		dp[i][1] = max(dp[i-1][0] + v[i], dp[i-2][0] + v[i]);
	}

	int ans = max(dp[n-1][0], dp[n-1][1]);

	cout << ans << endl;
	return 0;
}