#define _CRT_SECURE_NO_WARNINGS
#define MAX(a,b) (a>b ? a:b)
#include <stdio.h>
#include <stdlib.h>
int main()
{
int n;
int *s, *dp;
scanf("%d", &n);
s = (int *)malloc(sizeof(int) * n);
dp = (int *)malloc(sizeof(int) * n);
for(int i=0; i<n; i++)
{
scanf("%d", &s[i]);
printf("%d", &s[i]);
}
for(int i=0; i<n; i++)
{
if(i == 0)
{
dp[i] = s[0];
}
else if(i == 1)
{
dp[i] = s[0] + s[1];
}
else if(i == 2)
{
dp[i] = MAX(s[0]+s[2], s[1]+s[2]);
}
else
dp[i] = MAX(dp[i-3]+s[i-1]+s[i], dp[i-2]+s[i]);
}
printf("%d", dp[n-1]);
}