#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=2e5+10;
int n,a[N],f[2][N];
int dfs(int t,int x)
{
	if(x==n+1)return 0;
	if(f[t][x])return f[t][x];
	f[t][x]=max(dfs(t,x+1),dfs(t^1,x+1)+a[x]+(t&1)*a[x]);
	return f[t][x];
}
signed main()
{
	scanf("%lld",&n);
	for(int i=1;i<=n;i++)scanf("%lld",&a[i]);
	printf("%lld\n",dfs(0,1));
	return 0;
}