#include<stdio.h>
int main()
{
    int n,i;
    int books[100];
    if(scanf("%d",&n)!=1 || n<0)
    {
        printf("Invalid input");
        return 0;
    }
    for(i=0;i<n;i++)
    {
        if(scan("%d",&books[i])!=1)
        {
            printf("Invalid input");
            return 0;
        }
    }
    for(i=0;i<n;i+=2)
       printf("%d",books[i]);
    for(i=1;i<n;i+=2)
      printf("%d",books[i]);
 return 0;
}