#include <iostream>
#include <stdio.h>

using namespace std;

int v[100010];
int dp[100010];

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


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

    dp[0]=dp[1]=0;
    dp[2]=v[1]+v[2];
    dp[3]=v[2]+v[3];
    for(int i=4;i<=n+1;i++){
        dp[i]=(v[i]+v[i-1])+max(dp[i-3],dp[i-4]);
    }
    printf("%d",dp[n]);

    return 0;
}