#include <bits/stdc++.h>
using namespace std;
double get(pair<int, int> a, pair<int, int> b) {
  double ret = 0;
  int x = max(a.first, b.first);
  int y = min(a.second, b.second);
  if (x > y)
    return 0;
  else
    ret = (y - x + 1);
  return ret;
}
int main() {
  int i, n, j, k, till, now, pl, pr, vl, vr, Ka, siz;
  scanf("%d %d %d %d %d", &pl, &pr, &vl, &vr, &Ka);
  vector<int> v;
  pair<int, int> p1, p2;
  p1 = make_pair(pl, pr);
  p2 = make_pair(vl, vr);
  for (k = 1; k <= 9; k++) {
    till = (1 << k) - 1;
    for (i = 0; i <= till; i++) {
      now = 0;
      for (j = 0; j < k; j++) {
        now *= 10;
        if ((1 << j) & i)
          now += 7;
        else
          now += 4;
      }
      v.push_back(now);
    }
  }
  siz = v.size();
  sort(v.begin(), v.end());
  double lob, hor;
  hor = fabs(pr - pl + 1);
  hor *= fabs((double)(vr - vl + 1));
  lob = 0;
  for (i = 0; i <= (siz - Ka); i++) {
    j = i + Ka - 1;
    pair<int, int> l, r;
    if (i == 0)
      l = make_pair(1, v[i]);
    else
      l = make_pair(v[i - 1] + 1, v[i]);
    if (j == (siz - 1))
      r = make_pair(v[j], 1000000000);
    else
      r = make_pair(v[j], v[j + 1] - 1);
    if (l.second == r.first) {
      int f = l.second;
      r.first++;
      lob += get(l, p1) * get(r, p2);
      lob += get(l, p2) * get(r, p1);
      l.second--;
      r.first = f;
      r.second = f;
      lob += get(l, p1) * get(r, p2);
      lob += get(l, p2) * get(r, p1);
      if (vl <= f && f <= vr && pl <= f && f <= pr) lob++;
    } else {
      lob += get(l, p1) * get(r, p2);
      lob += get(l, p2) * get(r, p1);
    }
  }
  printf("%.12lf\n", lob / hor);
  return 0;
}
