#include<iostream>
#include<cstdio>
#include<string>
#include<vector>
#include<queue>
#include<set>
#include<sstream>
#include<algorithm>
using namespace std;

#define ALL(x) (x).begin(),(x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define rep(i,n) for(int i=0;i<n;i++)
#define rev(j,m) for(int j=1;j<=m;j++)


int n;
int dp[1000];
bool memo[1000];
int A[1000];

int solve(int a){
	if(a >= n)return 0;
	if(memo[a])return dp[a];
	
	int res = max(solve(a+1),A[a]+solve(a+2));
	
	memo[a]=true;
	return dp[a] = res;
}

int main(){
	cin >> n;
	rep(i,n)
		cin >> A[i];
	
	cout << solve(0) << endl;
	return 0;
}