> #include<iostream>
> #include<cstring>
> using namespace std;
> 
> int main(){
>     int n, i, j, t, r, length;
>     char str[200];
>     char a[100][20];
> 
>     while(cin>>n){
>         if(n==0)
>             break;
>         cin >> str;
>         length = strlen(str);
>         r = length/n;
>         t=0;
>         for(i=0;i<r;i++)
>             for(j=0;j<n;j++){
>                 if(i%2==0)
>                     a[i][j] = str[t];
>                 if(i%2!=0)
>                     a[i][n-1-j] = str[t];
>                 t++;
>             }
>         for(i=0;i<n;i++)
>             for(j=0;j<r;j++)
>                 cout << a[j][i];
>         cout << endl;
>     }
>     return 0;
> }