#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops")
const int N = 2e5 + 5;
const long long int mod = 1e9 + 7;
const long long int Mod = 998244353;
const long double Pi = acos(-1);
const long long int Inf = 4e18;
const long double Eps = 1e-9;
int dx[9] = {0, 1, -1, 0, 0, 1, 1, -1, -1};
int dy[9] = {0, 0, 0, 1, -1, 1, -1, 1, -1};
using namespace std;
long long int Intersection(long long int l1, long long int r1, long long int l2,
                           long long int r2) {
  return max(0LL, min(r1, r2) - max(l1, l2) + 1);
}
void TestCase() {
  long long int pl, pr, vl, vr, k, tot = 0;
  cin >> pl >> pr >> vl >> vr >> k;
  long double ans;
  vector<long long int> num;
  for (long long int len = 1; len <= 9; len++) {
    for (long long int i = 0; i < (1 << len); i++) {
      long long int p = 1, n = 0;
      for (long long int j = 0; j < len; j++) {
        if (i & (1 << j))
          n += 7 * p;
        else
          n += 4 * p;
        p = p * 10;
      }
      num.push_back(n);
    }
  }
  sort(num.begin(), num.end());
  num.insert(num.begin(), 0);
  for (long long int i = 1; i < (long long int)num.size(); i++) {
    if (i + k > (long long int)num.size()) continue;
    long long int a, b, c, d, up;
    if (i + k == (long long int)num.size())
      up = 1000000000;
    else
      up = num[i + k] - 1;
    a = Intersection(pl, pr, num[i - 1] + 1, num[i]);
    b = Intersection(vl, vr, num[i + k - 1], up);
    c = Intersection(vl, vr, num[i - 1] + 1, num[i]);
    d = Intersection(pl, pr, num[i + k - 1], up);
    tot += a * b + c * d;
    if (k == 1) {
      bool ok =
          ((num[i] >= pl && num[i] <= pr) && (num[i] >= vl && num[i] <= vr));
      if (ok) tot--;
    }
  }
  long double f = (long double)(tot) / ((vr - vl + 1) * (pr - pl + 1));
  cout << fixed << setprecision(10) << f;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  ;
  int T = 1;
  while (T--) {
    TestCase();
    cout << "\n";
  }
  return 0;
}
