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

int main(void){
    int n, v[1001];
    cin >> n;
    for(int i=0; i<n; i++){
        cin >> v[i];
    }
    if( n == 1 ){
        cout << v[0] << endl;
        return 0;
    }else if(n==2){
        if(v[0] < v[1]){
            cout << v[1] << endl;
        }else{
            cout << v[0] << endl;
        }
        return 0;
    }
    int dp[1001];
    dp[0] = v[0];
    dp[1] = v[1];
    dp[2] = v[0] + v[2];
    for(int i=3; i<n; i++){
        int tmp1 = max(dp[i-2]+v[i], dp[i-3]+v[i]);
        int tmp2 = max(dp[i-1], dp[i-2]);
        dp[i] = max(tmp1, tmp2);
    }
    cout << dp[n-1] << endl;
    return 0;
}