#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("cifre.in");
ofstream fout("cifre.out");

int main() {
    float a, b, c, k;
    long i, temp, nr = 0, nr2 = 0;

    fin >> a >> b >> c >> k;
    for(i = a; i <= b; i++) {
        temp = i;
        while(temp) {
            if(temp % 10 == c) {
                nr2++;
                if (nr2 == k)
                    temp = 0;
            }
            temp /= 10;
        }
        if(nr2 == k)
            nr++;
        nr2 = 0;
    }
    fout << nr / (b - a + 1);

    return 0;
}