#include<stdio.h>

int maxim,N,a[100010],v[100011];

int max(int a,int b)
{
    if(a>b)
    return a;
    return b;
}


int main()
{
freopen("oo.in","r",stdin);
freopen("oo.out","w",stdout);


scanf("%d",&N);



for(int i=1;i<=N;++i)
{
scanf("%d",&v[i]);
}

a[1]=v[1]+v[N];
a[2]=max(a[1],v[2]+v[1]);

for(int i=3;i<=N-2;++i)
    a[i]=max(a[i-1],a[i-3]+v[i]+v[i-1]);


maxim=a[N-2];

a[1]=0;
a[2]=v[1]+v[2];
for(int i=3;i<=N-1;++i)
    a[i]=max(a[i-1],a[i-3]+v[i]+v[i-1]);

a[1]=0;
a[2]=0;

if(a[N-1]>maxim)
maxim=a[N-1];

for(int i=3;i<=N;++i)
    a[i]=max(a[i-1],a[i-3]+v[i]+v[i-1]);

if(a[N]>maxim)
maxim=a[N];

printf("%d",maxim);
return 0;
}