#include <bits/stdc++.h>
using namespace std;
long long mm[2000];
int tt = 0;
void dfs(long long k) {
  if (k > 1000000000) return;
  mm[tt++] = k;
  dfs(k * 10 + 4);
  dfs(k * 10 + 7);
}
double jiao(long long s1, long long e1, long long s2, long long e2) {
  if (s1 < s2) s1 = s2;
  if (e1 > e2) e1 = e2;
  if (s1 > e1) return 0;
  return e1 - s1 + 1;
}
int main() {
  int a, b, i, j, k;
  long long pl, pr, vl, vr;
  double sum, ok, s1, s2;
  dfs(0);
  mm[tt++] = 99999999999;
  sort(mm, mm + tt);
  while (scanf("%I64d %I64d %I64d %I64d %d", &pl, &pr, &vl, &vr, &k) != EOF) {
    ok = 0;
    sum = (pr - pl + 1) * (vr - vl + 1);
    for (i = 1; i + k - 1 < tt; ++i) {
      if (k == 1 && mm[i] <= min(pr, vr) && mm[i] >= max(pl, vl)) ok--;
      j = i + k - 1;
      ok += jiao(mm[i - 1] + 1, mm[i], pl, pr) *
            jiao(mm[j], mm[j + 1] - 1, vl, vr);
      ok += jiao(mm[i - 1] + 1, mm[i], vl, vr) *
            jiao(mm[j], mm[j + 1] - 1, pl, pr);
    }
    printf("%.15lf\n", ok / sum);
  }
  return 0;
}
