#include <bits/stdc++.h>
using namespace std;
int a[1022];
int minusa = 0;
long long calcul(int pl, int pr, int vl, int vr, int k, int i) {
  int l1 = max((i == 0 ? min(pl, a[i]) : a[i - 1] + 1), pl);
  int r1 = min(a[i], pr);
  int l2 = max(a[i + k - 1], vl);
  int r2 = min((i + k == 1022 ? vr : a[i + k] - 1), vr);
  if (r1 >= l1 && r2 >= l2) {
    if (r1 == l2) {
      minusa++;
    }
    return (long long)(r1 - l1 + 1) * (r2 - l2 + 1);
  }
  return 0;
}
int main() {
  queue<int> q;
  q.push(4);
  q.push(7);
  int d = 1;
  int cnt = 0;
  while (!q.empty() && d < 10) {
    int size = q.size();
    while (size--) {
      int plucky = q.front();
      a[cnt] = plucky;
      q.pop();
      if (d < 9) {
        q.push(plucky * 10 + 4);
        q.push(plucky * 10 + 7);
      }
      cnt++;
    }
    d++;
  }
  int pl, pr, vl, vr, k;
  scanf("%d %d %d %d %d", &pl, &pr, &vl, &vr, &k);
  long long trueSpace = 0;
  for (int i = 0; i <= 1022 - k; i++) {
    minusa = 0;
    trueSpace += calcul(pl, pr, vl, vr, k, i);
    trueSpace += calcul(vl, vr, pl, pr, k, i);
    if (minusa == 2) {
      trueSpace--;
    }
  }
  double res = (double)trueSpace / ((long long)(pr - pl + 1) * (vr - vl + 1));
  printf("%.13lf", res);
  return 0;
}
