#include <bits/stdc++.h>
using namespace std;
long long int vl, vr, pl, pr, k, INF = 1e9 + 10;
vector<long long int> lucky;
void init() {
  long long int r;
  lucky.push_back(0);
  lucky.push_back(INF);
  for (long long int l = 1; l < 10; l++) {
    for (long long int i = 0; i < (1LL << l); i++) {
      r = 0;
      for (long long int j = 0; j < l; j++) {
        r = r * 10 + 4 + (1 & (i >> j)) * 3;
      }
      lucky.push_back(r);
    }
  }
  sort(lucky.begin(), lucky.end());
}
long long int intersect(long long int al, long long int ar, long long int bl,
                        long long int br) {
  return max(0LL, min(ar, br) - max(al, bl) + 1);
}
signed main() {
  cout << fixed << setprecision(10);
  init();
  cin >> vl >> vr >> pl >> pr >> k;
  long long int num = 0, sgn = 1, l, r;
  if (k == 1) {
    for (long long int i = 1; i < lucky.size() - k; i++) {
      l = lucky[i], r = lucky[i + k - 1];
      num += intersect(lucky[i - 1] + 1, lucky[i], vl, vr) *
             intersect(lucky[i + k - 1], lucky[i + k] - 1, pl, pr);
      num += intersect(lucky[i - 1] + 1, lucky[i], pl, pr) *
             intersect(lucky[i + k - 1], lucky[i + k] - 1, vl, vr);
      num -= intersect(lucky[i], lucky[i], pl, pr) *
             intersect(lucky[i + k - 1], lucky[i + k - 1], vl, vr);
    }
    cout << 1.0 * num / (vr - vl + 1) / (pr - pl + 1) << endl;
    return 0;
  }
  for (long long int i = 1; i < lucky.size() - k; i++) {
    l = lucky[i], r = lucky[i + k - 1];
    num += intersect(lucky[i - 1] + 1, lucky[i], vl, vr) *
           intersect(lucky[i + k - 1], lucky[i + k] - 1, pl, pr);
    num += intersect(lucky[i - 1] + 1, lucky[i], pl, pr) *
           intersect(lucky[i + k - 1], lucky[i + k] - 1, vl, vr);
  }
  cout << 1.0 * num / (vr - vl + 1) / (pr - pl + 1) << endl;
}
