#include <bits/stdc++.h>
const long long INF = 1e18;
const int N = 1e5 + 5, inf = 1e9, mod = 1e9 + 7;
using namespace std;
long double pl, pr, vl, vr, k;
vector<long double> l;
void gen(long double x) {
  if (x * 10 + 4 <= max(pr, vr)) {
    if (x * 10 + 4 >= min(pl, vl)) l.push_back(x * 10 + 4);
    gen(x * 10 + 4);
  }
  if (x * 10 + 7 <= max(pr, vr)) {
    if (x * 10 + 7 >= min(pl, vl)) l.push_back(x * 10 + 7);
    gen(x * 10 + 7);
  }
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> pl >> pr >> vl >> vr >> k;
  l.push_back(0);
  l.push_back(inf);
  gen(0);
  sort(l.begin(), l.end());
  if (l.size() - 2 < k) return cout << "0\n", 0;
  long double ans = 0.0;
  long double p = (pr - pl + 1), v = (vr - vl + 1);
  for (int i = 1; i < l.size() - k; i++) {
    if (pl <= l[i] && vr >= l[i + k - 1]) {
      long double tmp1 =
          max((long double)0,
              ((long double)min(pr, l[i]) - max(l[i - 1] + 1, pl) + 1) / p);
      long double tmp2 = max(
          (long double)0,
          ((long double)min(l[i + k] - 1, vr) - max(vl, l[i + k - 1]) + 1) / v);
      ans += tmp1 * tmp2;
    }
    if (vl <= l[i] && pr >= l[i + k - 1]) {
      long double tmp1 =
          max((long double)0,
              ((long double)min(vr, l[i]) - max(l[i - 1] + 1, vl) + 1) / v);
      long double tmp2 = max(
          (long double)0,
          ((long double)min(l[i + k] - 1, pr) - max(pl, l[i + k - 1]) + 1) / p);
      ans += tmp1 * tmp2;
    }
    if (pl <= l[i] && l[i] <= pr && vl <= l[i + k - 1] && l[i + k - 1] <= vr &&
        k == 1)
      ans -= (1.0 / p) * (1.0 / v);
  }
  cout << fixed << setprecision(10) << ans << '\n';
  return 0;
}
