#include <bits/stdc++.h>
using namespace std;
vector<long long> v;
long long vr, vl, pl, pr, k;
void dfs(long long x) {
  if (x >= 10000000000000LL) return;
  v.push_back(x);
  dfs(x * 10 + 4);
  dfs(x * 10 + 7);
}
long long getans(long long sx, long long sy, long long tx, long long ty) {
  if (tx <= sx && sy <= ty) return sy - sx + 1;
  if (sx <= tx && ty <= sy) return ty - tx + 1;
  if (sx > ty) return 0LL;
  if (tx > sy) return 0LL;
  return max(0LL, min(ty, sy) - max(sx, tx) + 1);
}
int main() {
  v.push_back(0);
  dfs(4);
  dfs(7);
  sort(v.begin(), v.end());
  cin >> pl >> pr >> vl >> vr >> k;
  long long res = 0;
  for (int i = 1; i < v.size(); i++) {
    if (v[i] > pr && v[i] > vr) break;
    if (i + k - 1 >= v.size()) break;
    long long nxt = v[i + k - 1];
    long long tl = v[i - 1] + 1;
    long long tr = v[i + k] - 1;
    long long suml = getans(tl, v[i], pl, pr);
    long long sumr = getans(v[i + k - 1], tr, vl, vr);
    res += suml * sumr;
    suml = getans(tl, v[i], vl, vr);
    sumr = getans(v[i + k - 1], tr, pl, pr);
    res += suml * sumr;
  }
  if (k == 1) {
    for (int i = 0; i < v.size(); i++)
      if (pl <= v[i] && v[i] <= pr && vl <= v[i] && v[i] <= vr) res--;
  }
  printf("%.12f\n", (double(res) / (pr - pl + 1)) / (vr - vl + 1));
  return 0;
}
