#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

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

    vector<int> dp(N+1);
    dp[0] = 0; dp[1] = a[1]; dp[2] = max(a[1],a[2]);
    for(int i=3;i<=N;i++){
        dp[i] = max(dp[i-2]+a[i],dp[i-1]);
    } 

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