#include<cstdio>
#include<cstring>

using namespace std;

const int nmax=1e5+5;

int v[nmax];

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

inline int dinamica(int start,int finish)
{
    int dp[nmax];
    memset(dp,0,sizeof(dp));
    int i;
    dp[start]=v[start];
    dp[start+1]=dp[start]+v[start+1];
    for(i=start+2;i<=finish;++i)
        dp[i]=max(dp[i-1],dp[i-3]+v[i]+v[i-1]);
    return dp[finish];
}


int main()
{
    freopen("oo.in","r",stdin);
    freopen("oo.out","w",stdout);
    int sol,n,i,j;
    scanf("%d",&n);
    for(i=1;i<=n;++i)
        scanf("%d",&v[i]);
    sol=0;
    sol=max(dinamica(1,n-1) , max(dinamica(2,n) , dinamica(3,n+1)));
    printf("%d",sol);
}