#include "bits/stdc++.h"
using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000

int dp[2][1020];

int main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
	int N; cin >> N;
	int a[1010];
	rep(i, N) cin >> a[i];
	rep(i, N){
		dp[0][i + 10] = max(dp[1][i + 9], dp[0][i + 9]);
		dp[1][i + 10] = max(dp[0][i + 9], dp[0][i + 8]) + a[i];
	}
	//rep(i, N + 10) {
	//	cout << i - 10 <<" " << dp[0][i] << " " << dp[1][i] << endl;
	//}
	cout << max(dp[0][N + 9], dp[1][N + 9]) << endl;


    return 0;
}