#include <iostream>
#include <vector>
#include <deque>
#define repeat(i,n) for (int i = 0; (i) < (n); ++(i))
#define repeat_from(i,m,n) for (int i = (m); (i) < (n); ++(i))
typedef long long ll;
using namespace std;
int main() {
    int n; cin >> n;
    vector<int> v(n); repeat (i,n) cin >> v[i];
    vector<int> dp(n+1);
    dp[0] =    0;
    dp[1] = v[0];
    repeat_from (i,1,n) {
        dp[i+1] = max(dp[i], dp[i-1] + v[i]);
    }
    cout << dp[n] << endl;
    return 0;
}