#include <bits/stdc++.h>
using namespace std;
long long luck[2000];
int num;
void DFS(long long k) {
  if (k > 1000000000) return;
  luck[num] = k;
  num++;
  DFS(k * 10 + 4);
  DFS(k * 10 + 7);
}
int main() {
  long long pl, pr, vl, vr;
  int k;
  num = 0;
  DFS(0);
  sort(luck, luck + num);
  luck[num] = 1000000000;
  while (scanf("%I64d%I64d%I64d%I64d%d", &pl, &pr, &vl, &vr, &k) != EOF) {
    double sum = 0;
    for (int i = 1; i + k - 1 < num; i++) {
      double l, r;
      l = 0;
      r = 0;
      if (luck[i] >= pl && luck[i - 1] < pr) {
        if (pr > luck[i]) {
          if (pl <= luck[i - 1])
            l = luck[i] - luck[i - 1];
          else
            l = luck[i] - pl + 1;
        } else {
          if (pl <= luck[i - 1])
            l = pr - luck[i - 1];
          else
            l = pr - pl + 1;
        }
      }
      if (luck[i + k - 1] <= vr && luck[i + k] > vl) {
        if (vl < luck[i + k - 1]) {
          if (vr >= luck[i + k])
            r = luck[i + k] - luck[i + k - 1];
          else
            r = vr - luck[i + k - 1] + 1;
        } else {
          if (vr >= luck[i + k])
            r = luck[i + k] - vl;
          else
            r = vr - vl + 1;
        }
      }
      sum += l * r;
      l = 0;
      r = 0;
      if (luck[i] >= vl && luck[i - 1] < vr) {
        if (vr > luck[i]) {
          if (vl <= luck[i - 1])
            l = luck[i] - luck[i - 1];
          else
            l = luck[i] - vl + 1;
        } else {
          if (vl <= luck[i - 1])
            l = vr - luck[i - 1];
          else
            l = vr - vl + 1;
        }
      }
      if (luck[i + k - 1] <= pr && luck[i + k] > pl) {
        if (pl < luck[i + k - 1]) {
          if (pr >= luck[i + k])
            r = luck[i + k] - luck[i + k - 1];
          else
            r = pr - luck[i + k - 1] + 1;
        } else {
          if (pr >= luck[i + k])
            r = luck[i + k] - pl;
          else
            r = pr - pl + 1;
        }
      }
      sum += l * r;
      if (k == 1) {
        if (luck[i] >= pl && luck[i] <= pr && luck[i] >= vl && luck[i] <= vr)
          sum -= 1;
      }
    }
    double ans = (pr - pl + 1) * (vr - vl + 1);
    ans = sum / ans;
    printf("%.12f\n", ans);
  }
  return 0;
}
