#include <bits/stdc++.h>
using namespace std;
int pl, pr, vl, vr, k;
vector<int> a;
void gen(long long x) {
  if (x > 1000000000) return;
  if (x != 0) a.push_back(x);
  gen(x * 10 + 4);
  gen(x * 10 + 7);
}
double get(int l, int r, int a, int b) {
  l = max(l, a);
  r = min(r, b);
  if (l > r) return 0.0;
  return (double)(r - l + 1) / (double)(b - a + 1);
}
int main() {
  cin >> pl >> pr >> vl >> vr >> k;
  gen(0);
  sort(a.begin(), a.end());
  int n = a.size();
  double res = 0.0;
  for (int i = 0; i < n; i++) {
    if (i + k - 1 >= n) continue;
    int x = a[i];
    int y = a[i + k - 1];
    int l1 = (i == 0 ? 1 : a[i - 1] + 1);
    int r1 = a[i];
    int l2 = a[i + k - 1];
    int r2 = (i + k - 1 == n - 1 ? 1000000000 : a[i + k] - 1);
    res += get(l1, r1, pl, pr) * get(l2, r2, vl, vr);
    res += get(l2, r2, pl, pr) * get(l1, r1, vl, vr);
    if (r1 == l2) res -= get(r1, l2, pl, pr) * get(r1, l2, vl, vr);
  }
  printf("%.10lf\n", res);
  return 0;
}
