11723-Numbering roads

#include<stdio.h>
int main()
{
    int r,n,a,i=1;
    while(scanf("%d %d", &r, &n)==2 && r!=0 && n!=0)
    {
        printf("Case %d: ",i);
        i++;
        a=(r-1)/n;
        if(a>26)
            printf("impossible\n");
        else
            printf("%d\n", a);
    }
    return 0;
}