#include <stdio.h>

int a[100010],d[100010],n,max,m,x,y;

int main()
{
    freopen("oo.in","rt",stdin);
    freopen("oo.out","wt",stdout);
    scanf("%d",&n);
    int i;
    for (i=1; i<=n; ++i) scanf("%d",&a[i]);
    max=0;
    d[0]=0;
    m=0;
    for (i=2; i<n; ++i)
    {
        max=d[i-2];
        if (max<d[i-1]) max=d[i-1];
        if (max<d[i-3]+a[i-1]+a[i] && i>2) max=d[i-3]+a[i-1]+a[i];
        if (i==2 && max<a[i-1]+a[i]) max=a[i-1]+a[i];
        d[i]=max;
    }
    if (d[n-1]>m) m=d[n-1];
    a[n+1]=a[1];
    for (i=1; i<=n; ++i) a[i]=a[i+1];
    max=0;
    d[0]=0;
    for (i=2; i<n; ++i)
    {
        max=d[i-2];
        if (max<d[i-1]) max=d[i-1];
        if (max<d[i-3]+a[i-1]+a[i] && i>2) max=d[i-3]+a[i-1]+a[i];
        if (i==2 && max<a[i-1]+a[i]) max=a[i-1]+a[i];
        d[i]=max;
    }
    if (d[n-1]>m) m=d[n-1];
    x=a[n-1];
    y=a[n];
    for (i=n; i>=3; --i) a[i]=a[i-2];
    a[1]=x;
    a[2]=y;
    max=0;
    d[0]=0;
    for (i=2; i<n; ++i)
    {
        max=d[i-2];
        if (max<d[i-1]) max=d[i-1];
        if (max<d[i-3]+a[i-1]+a[i] && i>2) max=d[i-3]+a[i-1]+a[i];
        if (i==2 && max<a[i-1]+a[i]) max=a[i-1]+a[i];
        d[i]=max;
    }
    if (d[n-1]>m) m=d[n-1];
    printf("%d\n",m);
    return 0;
}