#include <bits/stdc++.h>
using namespace std;
const long long P = (1000 * 1000 * 1000) + 7;
const int arrn = 4e5 + 3;
long long comp(long long l, long long r, long long pl, long long pr) {
  return max((long long)0, (min(r, pr) - max(l, pl) + 1));
}
void solve() {
  long long pl, pr, vl, vr, k;
  cin >> pl >> pr >> vl >> vr >> k;
  vector<long long> temp;
  for (int i = 1; i < 12; i++) {
    for (int j = 0; j < (1 << i); j++) {
      long long num = 0;
      long long pow = 1;
      for (int k = 0; k < i; k++) {
        if (j & (1 << k))
          num += 7 * pow;
        else
          num += 4 * pow;
        pow *= 10;
      }
      temp.push_back(num);
    }
  }
  long long out = 0;
  for (int i = 0; i + k - 1 < temp.size(); i++) {
    long long x1;
    long long x2;
    x1 = comp(((i == 0) ? 1 : (temp[i - 1] + 1)), temp[i], pl, pr);
    x2 = comp(temp[i + k - 1], ((i == temp.size()) ? P : (temp[i + k] - 1)), vl,
              vr);
    out += x1 * x2;
  }
  for (int i = 0; i + k - 1 < temp.size(); i++) {
    long long x1;
    long long x2;
    x1 = comp(((i == 0) ? 1 : (temp[i - 1] + 1)), temp[i], vl, vr);
    x2 = comp(temp[i + k - 1], ((i == temp.size()) ? P : (temp[i + k] - 1)), pl,
              pr);
    out += x1 * x2;
  }
  long long total = (pr - pl + 1) * (vr - vl + 1);
  if (k == 1) {
    long long x1 = max(pl, vl);
    long long x2 = min(pr, vr);
    if (x1 <= x2) {
      int temp1 = (upper_bound(temp.begin(), temp.end(), x2) -
                   lower_bound(temp.begin(), temp.end(), x1));
      out -= temp1;
    }
  }
  double ans = (double)out / total;
  cout << setprecision(10) << ans;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  int T;
  T = 1;
  while (T--) {
    solve();
  }
  return 0;
}
