#include<fstream.h>
long double s,ap=0,m,a,b,c,k,i,nr,x;
int main ()
{
ifstream in ("cifre.in");
ofstream out("cifre.out");
in>>a;
in>>b
in>>c;
in>>k;
for (i=a;i<=b;i++)
{ m++;
  while (nr!=0)
  { x=nr%10;
    if (x==c) {ap++;}
    else nr=nr/10; } }
if (ap>=k)
{ s=ap/m;
 out<<"probabilitatea e de "<<s; }
return 0;
}