#include <bits/stdc++.h>
using namespace std;
int l1, r1, l2, r2;
int k;
int mass[7027];
int tem[7027];
int coun;
void mergesort(int *a, int *b, int n) {
  int i, i0, i1, iRight, iEnd, width, j;
  for (width = 1; width < n; width *= 2)
    for (i = 0; i < n; i += width * 2) {
      i0 = i;
      i1 = iRight = min(i + width, n);
      iEnd = min(i + width * 2, n);
      for (j = i; j < iEnd; j++)
        if (i0 < iRight && (i1 == iEnd || a[i0] < a[i1]))
          b[j] = a[i0++];
        else
          b[j] = a[i1++];
      for (j = i; j < iEnd; j++) a[j] = b[j];
    }
}
int d[10];
void dfs(int x, int res) {
  mass[coun++] = res + d[x] * 4;
  mass[coun++] = res + d[x] * 7;
  if (x == 8) return;
  dfs(x + 1, res + d[x] * 4);
  dfs(x + 1, res + d[x] * 7);
}
int main() {
  cin >> l1 >> r1 >> l2 >> r2 >> k;
  long long ans = 0;
  int i, j;
  d[0] = 1;
  for (i = 1; i < 10; i++) d[i] = d[i - 1] * 10;
  dfs(0, 0);
  mergesort(mass, tem, coun);
  for (i = coun; i > 0; i--) mass[i] = mass[i - 1];
  mass[coun + 1] = 2000000000;
  mass[0] = -2000000000;
  for (i = 1; i + k <= coun + 1; i++) {
    if (mass[i] >= l1 && mass[i - 1] < r1)
      if (mass[i + k] > l2 && mass[i + k - 1] <= r2)
        ans += (long long)(min(r1, mass[i]) - max(l1, mass[i - 1] + 1) + 1) *
               (min(r2, mass[i + k] - 1) - max(l2, mass[i + k - 1]) + 1);
    if (mass[i] >= l2 && mass[i - 1] < r2)
      if (mass[i + k] > l1 && mass[i + k - 1] <= r1)
        ans += (long long)(min(r2, mass[i]) - max(l2, mass[i - 1] + 1) + 1) *
               (min(r1, mass[i + k] - 1) - max(l1, mass[i + k - 1]) + 1);
  }
  if (k == 1) {
    for (i = 1; i <= coun; i++)
      if (l1 <= mass[i] && mass[i] <= r1 && l2 <= mass[i] && mass[i] <= r2)
        ans--;
  }
  long long del = (long long)(r1 - l1 + 1) * (r2 - l2 + 1);
  cout << setprecision(20) << (long double)ans / (long double)del << endl;
  return 0;
}
