#include<bits/stdc++.h>
#define rep(i,a,n) for (int i = a; i < n; i++)
#define per(i,n,a) for (int i = n - 1; i >= a; i--)
using namespace std;

int v[1111], dp[1111];
int main() {
    int n;
    cin >> n;
    rep(i, 0, n) {
        cin >> v[i];
    }
    dp[0] = v[0];
    dp[1] = max(v[1], v[0]);
    rep(i, 2, n) {
        dp[i] = max(dp[i - 1], dp[i - 2] + v[i]);
    }
    cout << dp[n - 1] << endl;
}