#include <cstdio>

using namespace std;
int maxi(int a, int b){
 if(a>b) return a;
  else return b;
}
int n,x,a[100001],d[100001],i;
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]);
    d[1]=0;
    d[2]=0;
    d[3]=a[2]+a[3];
    for(i=4;i<=n;++i)
     d[i]=maxi(d[i-1],a[i]+a[i-1]+d[i-3]);
    x=d[n];
    printf("%d",x);


    return 0;
}