#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <queue>
#include <set>
#include <map>
using namespace std;

#define FOR(i, s, e) for (int i = (s); i <= (e); i++)


int n;
int v[1010];

int dp[1010];

int main()
{
    cin >> n;

    FOR(i,0,n - 1) cin >> v[i];

    FOR(i,0,n - 1)
    {

        //eat
        if(i == 0)
        {
            dp[i + 1] = max(dp[i + 1],v[i]);
        }
        else if(i == 1)
        {
            dp[i + 1] = max(dp[i + 1],dp[i]);
            dp[i + 1] = max(dp[i + 1] , v[i]);
        }
        else
        {
            dp[i + 1] = max(dp[i + 1],dp[i]);
            dp[i + 1] = max(dp[i + 1],dp[i - 1] + v[i]);
        }
    }

    cout << dp[n] << endl;
    return 0;
}