#include <bits/stdc++.h>
using namespace std;
const int Max = 1000000100;
vector<long long> s;
void dfs(long long temp) {
  if (temp > Max) {
    return;
  }
  long long x = temp * 10 + 4;
  if (temp > Max) {
    return;
  }
  s.push_back(x);
  dfs(x);
  long long y = temp * 10 + 7;
  if (temp > Max) {
    return;
  }
  s.push_back(y);
  dfs(y);
}
int main() {
  dfs(0);
  s.push_back(0);
  sort(s.begin(), s.end());
  long long l, r, x, y;
  int n;
  cin >> l >> r >> x >> y >> n;
  long long temp = l > x ? x : l;
  int i = lower_bound(s.begin(), s.end(), temp) - s.begin();
  double sum = 0;
  while (true) {
    long long a = s[i - 1] + 1;
    long long b = s[i];
    long long c = s[i + n - 1];
    long long d = s[i + n] - 1;
    if (a > r && a > y) break;
    if (c > r && c > y) break;
    long long A = a > l ? a : l;
    long long B = b < r ? b : r;
    long long C = c > x ? c : x;
    long long D = d < y ? d : y;
    int shabi;
    int z = 0;
    if (n == 1 && B == C) {
      int o = lower_bound(s.begin(), s.end(), B) - s.begin();
      if (s[o] == B) z = 1;
    }
    if (z) shabi = D;
    if (A <= B && C <= D) {
      if (z)
        sum += (double)(B - A) / (double)(r - l + 1) * (double)(D - C + 1) /
               (double)(y - x + 1);
      else
        sum += (double)(B - A + 1) / (double)(r - l + 1) * (double)(D - C + 1) /
               (double)(y - x + 1);
    }
    A = a > x ? a : x;
    B = b < y ? b : y;
    C = c > l ? c : l;
    D = d < r ? d : r;
    if (A <= B && C <= D) {
      if (z)
        sum += (double)(B - A + 1) / (double)(y - x + 1) * (double)(D - C) /
               (double)(r - l + 1);
      else
        sum += (double)(B - A + 1) / (double)(y - x + 1) * (double)(D - C + 1) /
               (double)(r - l + 1);
    }
    if (z) {
      sum += (double)(shabi - A + 1) / (double)(y - x + 1) * (double)(1) /
             (double)(r - l + 1);
    }
    i++;
  }
  printf("%.12lf", sum);
  return 0;
}
