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

int main(){
    int N;
    cin>>N;
    vector<int> a(N+1);
    vector<int> dp(N+1);

    a[0] = 0;

    for(int i=1;i<=N;i++){
        cin>>a[i];
    }

    dp[0] = 0;
    dp[1] = a[1];

    for(int i=2;i<=N;i++){
        dp[i] = max(dp[i-1],dp[i-2]+a[i]);
    }

    cout<<dp[N]<<endl;
}