#include<bits/stdc++.h>
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

using namespace std;
typedef long long int ll;

int dp[2000];

int main(){
    int i,j,k,l;
    int m,n;
    
    cin >> n;
    
    int in;
    
    for (i=0;i<n;i++){
        scanf("%d",&in);
        if (i==0){dp[0]=in;continue;}
        if (i==1){dp[1]=max(dp[0],in);continue;}
        dp[i]=max(dp[i-1],dp[i-2]+in);
    }
    cout<<dp[n-1]<<endl;
    
    return 0;
}