#include <bits/stdc++.h>
using namespace std;
long long p1, p2, v1, v2, k, lk[100005], top, ans, all;
inline long long read() {
  long long ret = 0, ff = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-') ff = -ff;
    ch = getchar();
  }
  while (isdigit(ch)) {
    ret = (ret << 3) + (ret << 1) + (ch ^ 48);
    ch = getchar();
  }
  return ret * ff;
}
void dfs(long long x, long long s) {
  lk[++top] = s;
  if (x == 10) return;
  dfs(x + 1, s * 10 + 4);
  dfs(x + 1, s * 10 + 7);
}
inline long long calc(long long x, long long y, long long a, long long b) {
  if (a >= x && b <= y) return b - a + 1;
  if (x >= a && y <= b) return y - x + 1;
  if (x <= a && a <= y && y <= b) return y - a + 1;
  if (a <= x && x <= b && b <= y) return b - x + 1;
  if (y <= a || b <= x) return 0;
}
signed main() {
  dfs(1, 0);
  sort(lk + 1, lk + top + 1);
  lk[0] = 0, lk[top + 1] = 2e9;
  p1 = read(), p2 = read(), v1 = read(), v2 = read(), k = read();
  all = (p2 - p1 + 1) * (v2 - v1 + 1);
  if (k == 1) {
    for (long long i = 1; i <= top; i++) {
      ans += calc(lk[i - 1] + 1, lk[i], p1, p2) *
             calc(lk[i], lk[i + 1] - 1, v1, v2);
      swap(p1, v1), swap(p2, v2);
      ans += calc(lk[i - 1] + 1, lk[i], p1, p2) *
             calc(lk[i], lk[i + 1] - 1, v1, v2);
      swap(p1, v1), swap(p2, v2);
      if (lk[i] >= p1 && lk[i] <= p2 && lk[i] >= v1 && lk[i] <= v2) ans--;
    }
    double res;
    res = (double)ans / (double)all;
    printf("%.12lf", res);
    return 0;
  }
  for (long long i = 1; i + k - 1 <= top; i++) {
    ans += calc(lk[i - 1] + 1, lk[i], p1, p2) *
           calc(lk[i + k - 1], lk[i + k] - 1, v1, v2);
    swap(p1, v1), swap(p2, v2);
    ans += calc(lk[i - 1] + 1, lk[i], p1, p2) *
           calc(lk[i + k - 1], lk[i + k] - 1, v1, v2);
    swap(p1, v1), swap(p2, v2);
  }
  double res;
  res = (double)ans / (double)all;
  printf("%.12lf", res);
  return 0;
}
