#include <fstream>
using namespace std;

int main()
{
	unsigned int   contor(0), j(0), i, x,
				   A, B, C;
	unsigned short K;

	ifstream g("cifre.in");
	ofstream f("cifre.out");

	g >> A >> B >> C >> K;

	for(i = A; i <= B; i++)
	{
		x = i;
		while(x)
		{
			if(x % 10 == C)
			{
				++j;
				break;
			}
			x = x / 10;
		}
	}

	f << (static_cast<double>(j) / B);
	
	g.close();
	f.close();
	return 0;
}