#include<fstream.h>
#include<iomanip.h>

unsigned short verif(unsigned long,unsigned short,unsigned short);

main()
{
	unsigned long A,B,i,total=0,contor=0;
	double long posibilitate;
	unsigned short K,C;

	ifstream In("cifre.in");
	In>>A>>B>>K>>C;
	In.close();
	for(i=A;i<=B;i++)
	{

	       total++;
	       if(verif(i,K,C)) contor++;

	}

	posibilitate=(double long)(contor/total);

	ofstream Out("cifre.out");
	Out<<setprecision(4)<<posibilitate<<"\n";
	Out.close();

	return 0;

}

unsigned short verif(unsigned long nr,unsigned short aparitii,unsigned short cifr)
{
	unsigned short contor=0;
	while(nr>0)
	{
		if(nr%10==cifr) contor++;
		nr/=10;
	}

	if(contor>=aparitii) return 1;
	return 0;

}