#include <bits/stdc++.h>
using namespace std;
long long n1, n2, m1, m2, left, right, k;
int MAXV = 1000000000;
int n = 0;
vector<int> a;
void generate(long long x) {
  if (x <= MAXV) {
    if (x != 0) a.push_back(x);
  } else {
    return;
  }
  x = x * 10 + 4;
  generate(x);
  x = x - 4 + 7;
  generate(x);
}
long long g(long long l1, long long l2, long long n, long long m) {
  long long minx = max(l1, n), maxx = min(l2, m);
  if (minx <= maxx) return maxx - minx + 1;
  return 0;
}
long long f(long long leftMin, long long leftMax, long long rightMin,
            long long rightMax, long long n1, long long n2, long long m1,
            long long m2) {
  return g(leftMin, leftMax, n1, n2) * g(rightMin, rightMax, m1, m2);
}
int main() {
  cin >> n1 >> n2 >> m1 >> m2 >> k;
  MAXV = max(n2, m2);
  generate(0);
  n = a.size();
  sort(a.begin(), a.end());
  long long sum = 0;
  long long cases = (n2 - n1 + 1) * (m2 - m1 + 1);
  for (auto i = 0; i < n - k + 1; i++) {
    long long leftMax = a[i], rightMin = a[i + k - 1];
    long long leftMin = i == 0 ? 1 : a[i - 1] + 1;
    leftMin = max(leftMin, min(n1, m1));
    long long rightMax = (i + k) == n ? MAXV : a[i + k] - 1;
    rightMax = min(rightMax, max(n2, m2));
    if (rightMin > rightMax || leftMin > leftMax || leftMax > rightMin)
      continue;
    sum += f(leftMin, leftMax, rightMin, rightMax, n1, n2, m1, m2);
    sum += f(leftMin, leftMax, rightMin, rightMax, m1, m2, n1, n2);
    if (k == 1) sum -= f(a[i], a[i], a[i], a[i], n1, n2, m1, m2);
  }
  cout << setprecision(9);
  cout << fixed << ((double)sum / (double)cases);
}
