#include <cstdio>
#include <string>
#include <vector>
#include <iostream>
using namespace std;

int dp[1010];

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    
    int N; cin >> N;
    int V[1010];
    for (int i = 0; i < N; ++i) cin >> V[i];
    dp[0] = 0;
    dp[1] = V[0];

    for (int i = 2; i <= N; ++i) {
        dp[i] = max(dp[i-2] + V[i-1], dp[i-1]);
    }

    cout << dp[N] << endl;
}