#include <bits/stdc++.h>
using namespace std;
 
#define vi vector<int>
#define vs vector<string>
#define int long long int
#define pii pair<int,int>
#define pb push_back
#define f(i,a,b) for(int i=a;i<b;i++)
#define ff first
#define s second
#define nl cout<<endl;
#define print(a) cout<<a<<"\n";
#define all(a) (a).begin(), (a).end()
#define parr(a) f(mnb,0,a.size()){cout<<a[mnb]<<" ";}cout<<endl;
#define rarr(a) f(yon,0,a.size()){cin>>a[yon];}
#define imx INT_MAX
#define imn INT_MIN
#define YN(a) cout << ((a)? "YES\n" : "NO\n");
const int MOD = 1e9+7;

void solve(){
    int n;
    cin >> n;
    vi A(n);
    rarr(A);

    vi dp(n + 1);
    dp[0] = A[0];

    f(i,1,n){
        if(i >= 2)
            dp[i] = max(A[i] + dp[i - 2], dp[i - 1]);
        else dp[i] = max(A[i], dp[i - 1]);
    }

    //parr(dp)
    cout << dp[n - 1] << endl;

}



signed main(){

ios_base::sync_with_stdio(false);
cin.tie(NULL);

int t=1;
//	cin>>t;
while(t--){
	solve();
}

}