#include<iostream>
#include<vector>
#include<string>
#include<algorithm>	
#include<map>
#include<set>
#include<utility>
#include<cmath>
#include<cstring>
#include<queue>
#include<stack>
#include<cstdio>
#include<sstream>
#include<iomanip>
#include<assert.h>
#include<ctime>
#include<cstdlib>
#include<numeric>
using namespace std;
typedef long long ll;
#define loop(i,a,b) for(ll i=a;i<b;i++)
#define rloop(i,a,b) for(int i=a;i>=b;i--)
const int inf=1e8;
const ll INF=1e16;
#define MOD 1000000007
#define mod 1000000009
#define m 1000003


int main(){
	int n;
	cin>>n;
	vector<int> v(n);
	loop(i,0,n){
		cin>>v[i];
	}
	vector< vector<int> > dp(n,vector<int>(2));
	dp[0][0]=0;dp[0][1]=v[0];
	loop(i,0,n-1){
		dp[i+1][0]=max(dp[i][1],dp[i][0]);
		dp[i+1][1]=max(dp[i][1],dp[i][0]+v[i+1]);
	}
	cout<<max(dp[n-1][0],dp[n-1][1])<<"\n";
}