#include <bits/stdc++.h>
using namespace std;
template <class T>
using vec = vector<T>;
const long long inf = numeric_limits<long long>::max() >> 1;
const long long infll = numeric_limits<long long>::max() >> 1;
const long long N = 1e5 + 1;
long long pl, pr, vl, vr, k;
long long ans;
vec<long long> lucky;
void input() { cin >> pl >> pr >> vl >> vr >> k; }
void generate(long long d, long long i) {
  if (i == 10) {
    return;
  }
  lucky.push_back(d);
  generate(10 * d + 4, i + 1);
  generate(10 * d + 7, i + 1);
}
void solve() {
  generate(0, 0);
  sort((lucky).begin(), (lucky).end());
  lucky.push_back(1e9);
  for (long long i = 1; i + k < (long long)((lucky).size()); ++i) {
    long long lx = max(pl, lucky[i - 1] + 1);
    long long ly = min(pr, lucky[i]);
    long long rx = max(vl, lucky[i + k - 1]);
    long long ry = min(vr, lucky[i + k] - 1);
    long long l = max(0ll, ly - lx + 1);
    long long r = max(0ll, ry - rx + 1);
    ans += l * r;
  }
  for (long long i = 1; i + k < (long long)((lucky).size()); ++i) {
    long long lx = max(vl, lucky[i - 1] + 1);
    long long ly = min(vr, lucky[i]);
    long long rx = max(pl, lucky[i + k - 1]);
    long long ry = min(pr, lucky[i + k] - 1);
    long long l = max(0ll, ly - lx + 1);
    long long r = max(0ll, ry - rx + 1);
    ans += l * r;
  }
  if (k == 1) {
    for (long long i = 1; i < (long long)((lucky).size()) - 1; ++i) {
      if (lucky[i] >= pl && lucky[i] <= pr && lucky[i] >= vl &&
          lucky[i] <= vr) {
        ans--;
      }
    }
  }
  cout << fixed << setprecision(9)
       << (double)ans / ((pr - pl + 1) * (vr - vl + 1)) << "\n";
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  input();
  solve();
}
