# include <cstdio>
# include <algorithm>
# define MAXN 100005
using namespace std;
int a[MAXN], s[MAXN][2];
int i,n;
int main()
{
    freopen("oo.in","r",stdin);
    freopen("oo.out","w",stdout);
    scanf("%d", &n);
    for (i=1; i<=n; ++i) scanf("%d",&a[i]);
    for (i=2; i<=n-1; ++i)
    {
        s[i][0]=max(a[i-1]+a[i]+s[i-3][0],s[i-1][0]);
        s[i][1]=max(s[i-1][0],s[i-1][1]);
    }
    s[n][0]=max(s[n-1][0],s[n-1][1]);
    printf("%d",s[n][0]);
    fclose(stdin);
    fclose(stdout);
    return 0;
}