#include <bits/stdc++.h>
using namespace std;
int n, k;
int a[1200];
void gen(int x, int y) {
  a[n++] = x;
  if (y == 9) return;
  gen(x * 10 + 4, y + 1);
  gen(x * 10 + 7, y + 1);
}
long long cross(int l1, int r1, int l2, int r2) {
  int l, r;
  l = max(l1, l2);
  r = min(r1, r2);
  if (l > r)
    return 0;
  else
    return (long long)(r - l + 1);
}
long long cal(int l1, int r1, int l2, int r2) {
  int i;
  long long v1, v2, res = 0;
  for (i = 1; i + k < n; i++) {
    v1 = cross(a[i - 1] + 1, a[i], l1, r1);
    v2 = cross(a[i + k - 1], a[i + k] - 1, l2, r2);
    long long temp = v1 * v2;
    res += temp;
  }
  return res;
}
int main() {
  gen(0, 0);
  sort(a, a + n);
  a[n++] = 1000000001;
  int l1, r1, l2, r2;
  scanf("%d%d%d%d%d", &l1, &r1, &l2, &r2, &k);
  long long y = (long long)(r1 - l1 + 1) * (long long)(r2 - l2 + 1);
  long long x = cal(l1, r1, l2, r2) + cal(l2, r2, l1, r1);
  if (k == 1)
    for (int i = 1; i < n - 1; i++)
      if (l1 <= a[i] && a[i] <= r1 && l2 <= a[i] && a[i] <= r2) x--;
  printf("%.15f\n", (double)x / (double)y);
  return 0;
}
