#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

#define RREP(i,s,e) for (i = e-1; i >= s; i--)
#define rrep(i,n) RREP(i,0,n)
#define REP(i,s,e) for (i = s; i < e; i++)
#define rep(i,n) REP(i,0,n)
#define INF 1e8

typedef long long ll;

int main() {
    int i, n;
    int v[1000];
    int dp[1000];
    cin >> n;
    rep (i,n) cin >> v[i];
    dp[0] = v[0];
    rep (i,n) {
        if (i >= 3)
            dp[i] = max({dp[i-1],dp[i-2]+v[i],dp[i-3]+v[i]});
        else if (i == 2)
            dp[i] = max(dp[i-1],dp[i-2]+v[i]);
        else
            dp[i] = v[i];
    }
    cout << dp[n-1] << endl;
    return 0;
}