#include <bits/stdc++.h>
using namespace std;
using LL = long long;
const int M = 1e5 + 5;
const int N = 1e2 + 2;
const int mo = 998244353;
int a[M], cnt;
void init() {
  a[cnt++] = 0;
  for (int n = 1; n <= 9; n++) {
    int ls = (1 << n);
    for (int i = 0; i < ls; i++) {
      int res = 0;
      for (int j = 0; j < n; j++) {
        if (i & (1 << j))
          res = res * 10 + 7;
        else
          res = res * 10 + 4;
      }
      a[cnt++] = res;
    }
  }
  a[cnt++] = 1e9 + 1;
  sort(a, a + cnt);
}
int main() {
  init();
  int pl, pr, vl, vr, k;
  scanf("%d%d%d%d%d", &pl, &pr, &vl, &vr, &k);
  double len1 = pr - pl + 1, len2 = vr - vl + 1;
  double res = 0;
  for (int i = 0; i + k < cnt; i++) {
    if (a[i + 1] >= pl && pr > a[i]) {
      if (a[i + k + 1] > vl && vr >= a[i + k]) {
        double low1 = max(pl, a[i] + 1), up1 = min(a[i + 1], pr);
        double low2 = max(a[i + k], vl), up2 = min(a[i + k + 1] - 1, vr);
        res += ((up1 - low1 + 1) / len1) * ((up2 - low2 + 1) / len2);
      }
    }
    if (a[i + 1] >= vl && vr > a[i]) {
      if (a[i + k + 1] > pl && pr >= a[i + k]) {
        double low1 = max(vl, a[i] + 1), up1 = min(a[i + 1], vr);
        double low2 = max(a[i + k], pl), up2 = min(a[i + k + 1] - 1, pr);
        res += ((up1 - low1 + 1) / len2) * ((up2 - low2 + 1) / len1);
      }
    }
  }
  if (k == 1) {
    for (int i = 1; i + 1 < cnt; i++) {
      if (a[i] >= pl && a[i] <= pr && a[i] >= vl && a[i] <= vr)
        res -= (1.0 / len1) * (1.0 / len2);
    }
  }
  printf("%.10f\n", res);
  return 0;
}
