#include <bits/stdc++.h>
using namespace std;
const int mod = 1000000007;
const int inf = 50000000;
const int maxn = 100010;
const long long lim = 5000000001;
vector<long long> lucky;
int pl, pr, vl, vr;
void generate(long long cur) {
  lucky.push_back(cur);
  long long nxt = cur;
  nxt = nxt * 10 + 4;
  if (nxt < lim) generate(nxt);
  nxt = cur;
  nxt = nxt * 10 + 7;
  if (nxt < lim) generate(nxt);
}
long long find_common(long long x1, long long y1, long long x2, long long y2) {
  long long x, y;
  y = min(y1, y2);
  x = max(x1, x2);
  return max(0ll, y - x + 1);
}
int main() {
  generate(0);
  sort(lucky.begin(), lucky.end());
  int i, k;
  double ans, x, y, p1, p2, cnt1, cnt2;
  ans = 0;
  scanf("%d%d%d%d%d", &pl, &pr, &vl, &vr, &k);
  p1 = (double)1.0 / (pr - pl + 1);
  p2 = (double)1.0 / (vr - vl + 1);
  for (i = 1; i + k <= lucky.size(); i++) {
    if (lucky[i + k - 1] > pr && lucky[i + k - 1] > vr) break;
    cnt1 = find_common(pl, pr, lucky[i - 1] + 1, lucky[i]);
    cnt2 = find_common(vl, vr, lucky[i + k - 1], lucky[i + k] - 1);
    x = (double)cnt1 * p1;
    y = (double)cnt2 * p2;
    ans = (ans + (x * y));
    cnt1 = find_common(pl, pr, lucky[i + k - 1], lucky[i + k] - 1);
    cnt2 = find_common(vl, vr, lucky[i - 1] + 1, lucky[i]);
    x = (double)cnt1 * p1;
    y = (double)cnt2 * p2;
    ans = (ans + (x * y));
    if (k == 1) {
      cnt1 = find_common(pl, pr, lucky[i], lucky[i]);
      cnt2 = find_common(vl, vr, lucky[i], lucky[i]);
      x = (double)cnt1 * p1;
      y = (double)cnt2 * p2;
      ans = (ans - (x * y));
    }
  }
  printf("%.12lf\n", ans);
  return 0;
}
