#include <bits/stdc++.h>
using namespace std;
vector<int> luck;
void lucky(long long v) {
  if (v > 1e9) return;
  luck.push_back(v);
  lucky(v * 10 + 4);
  lucky(v * 10 + 7);
}
long long intersect(int a, int b, int x, int y) {
  a = max(a, x);
  b = min(b, y);
  return max(0ll, 1ll * (b - a + 1));
}
pair<int, int> inter(int a, int b, int x, int y) {
  a = max(a, x);
  b = min(b, y);
  if (a <= b) return make_pair(a, b);
  return make_pair(0, -1);
}
int main() {
  lucky(4);
  lucky(7);
  int a, b, x, y, k;
  scanf("%d %d %d %d %d", &a, &b, &x, &y, &k);
  luck.push_back(0);
  luck.push_back(1e9 + 5);
  sort(luck.begin(), luck.end());
  long long t = 0;
  for (int i = 1; i + k < (int)luck.size(); ++i) {
    t += intersect(a, b, luck[i - 1] + 1, luck[i]) *
         intersect(x, y, luck[i + k - 1], luck[i + k] - 1);
    t += intersect(x, y, luck[i - 1] + 1, luck[i]) *
         intersect(a, b, luck[i + k - 1], luck[i + k] - 1);
    pair<int, int> p1 = inter(a, b, luck[i - 1] + 1, luck[i]);
    pair<int, int> p2 = inter(x, y, luck[i + k - 1], luck[i + k] - 1);
    pair<int, int> p3 = inter(x, y, luck[i - 1] + 1, luck[i]);
    pair<int, int> p4 = inter(a, b, luck[i + k - 1], luck[i + k] - 1);
    p1 = inter(p1.first, p1.second, p2.first, p2.second);
    p3 = inter(p3.first, p3.second, p4.first, p4.second);
    p1 = inter(p1.first, p1.second, p3.first, p3.second);
    t -= (1ll * p1.second - p1.first + 1) * (1ll * p1.second - p1.first + 1);
  }
  printf("%.15lf", t * 1.0 / (1ll * (y - x + 1) * (b - a + 1)));
}
