#include <cstdio>
#include <cstring>
using namespace std;
int v[100001],f[100001],nu[100001],i,n;
int maX(int x,int y)
{
    if (x>y) return x;
    else return y;
}
int main()
{
    freopen("oo.in","r",stdin);
    freopen("oo.out","w",stdout);
    scanf("%d",&n);
    for (i=1; i<=n; i++) scanf("%d",&v[i]);
    for (i=2; i<=n; i++)
    {
        if (i!=n)
            f[i]=maX(v[i-1]+v[i]+f[i-3],f[i-1]);
        nu[i]=maX(f[i-1],nu[i-1]);
    }
    printf("%d",nu[n]);
    return 0;
}