#include <bits/stdc++.h>
#define REP(i,n) for(int i = 0; i < (int)(n); ++i)
using namespace std;

int main() {
    int N, t;
    vector<int> V;
    cin >> N;
    REP(i,N){
        cin >> t;
        V.push_back(t);
    }
    int dp[N+1];
    dp[0] = V[0];
    dp[1] = max(V[0],V[1]);
    for(int i=2;i<N;i++){
        dp[i] = max(dp[i-1],V[i]+dp[i-2]);
    }
    cout << dp[N-1] << endl;
    return 0;
}