#include <iostream>

using namespace std;


int main(){
    int memo[1001];
    int N;
    cin>>N;
    memo[0]=0;

    for(int i=1; i<=N;i++){
        int v;
        cin>>v;
        if(i==1){
            memo[i] = v;
        }else {
            memo[i] = max(memo[i-1], memo[i-2] + v);
        }
    }
    
    cout<<memo[N]<<endl;
}