#include <bits/stdc++.h>
using namespace std;
int digit[2] = {4, 7};
vector<int> num;
int p1, p2, v1, v2, k;
void ini(long long int x) {
  if (x * 10 > (10000 * 100000)) return;
  for (int i(0); i < 2; ++i) {
    num.push_back(x * 10 + digit[i]);
    ini(x * 10 + digit[i]);
  }
  return;
}
double get_num(int si, int di) {
  double ans = 0;
  if (num[si - 1] > p2 || num[di + 1] < v1 || num[si - 1] > v2) {
    ans = 0;
  } else {
    bool flag1 = false, flag2 = false;
    if (num[di] <= v2 && num[si] >= p1) {
      double sec2 = min(num[di + 1], v2), sec1 = max(num[di], v1);
      double fir1 = max(num[si - 1], p1), fir2 = min(num[si], p2);
      if (num[di + 1] > v2) sec2++;
      if (num[si - 1] < p1) fir1--;
      ans += (sec2 - sec1) * (fir2 - fir1);
      flag1 = true;
    }
    if (num[di] <= p2 && num[si] >= v1) {
      double sec2 = min(num[di + 1], p2), sec1 = num[di];
      double fir1 = max(num[si - 1], v1), fir2 = min(num[si], v2);
      if (num[si - 1] < v1) fir1--;
      if (num[di + 1] > p2) sec2++;
      ans += (sec2 - sec1) * (fir2 - fir1);
      flag2 = true;
    }
    if (num[di] == num[si] && (flag1 && flag2)) ans--;
  }
  return ans;
}
int main() {
  scanf("%d%d%d%d%d", &p1, &p2, &v1, &v2, &k);
  ini(0);
  num.push_back(-1);
  num.push_back(1000000009);
  sort(num.begin(), num.end());
  if (p1 > v1) {
    swap(p1, v1);
    swap(p2, v2);
  }
  int now(-1), end(-1);
  for (int i(0); i < num.size(); ++i) {
    if (num[i] > max(p2, v2)) {
      end = i;
      break;
    }
    if (now != -1) continue;
    if (num[i] <= max(p2, v2) && num[i] >= min(p1, v1)) {
      now = i;
    }
  }
  if (now == -1) {
    cout << 0.000000 << endl;
    return 0;
  } else {
    if (end - now < k) {
      cout << 0.0000000 << endl;
      return 0;
    }
  }
  double ans = 0;
  for (int i(now); i < end && i + k - 1 < end; ++i) {
    int j = i + k - 1;
    ans += get_num(i, j);
  }
  double div = (p2 - p1 + 1);
  div *= (v2 - v1 + 1);
  ans /= div;
  if (ans > 1) ans = 1;
  printf("%.9lf\n", ans);
  return 0;
}
