#include <bits/stdc++.h>
using namespace std;
int n, i, k;
long long pl, pr, vl, vr, minp, maxp, minv, maxv;
long long lucky[2000];
long long numerator, denumerator;
void generate_lucky(long long me) {
  lucky[++n] = me;
  if (me * 10 + 4 <= 1000000000) generate_lucky(10 * me + 4);
  if (me + 10 + 7 <= 1000000000) generate_lucky(10 * me + 7);
}
long long intersection(long long l1, long long r1, long long l2, long long r2) {
  return (max(0LL, min(r1, r2) - max(l1, l2) + 1));
}
int main(int argc, char const *argv[]) {
  scanf("%lld%lld%lld%lld%d", &pl, &pr, &vl, &vr, &k);
  generate_lucky(4), generate_lucky(7);
  sort(lucky + 1, lucky + n + 1);
  numerator = 0;
  denumerator = (pr - pl + 1) * (vr - vl + 1);
  for (i = 1; i <= n - k + 1; ++i) {
    if (lucky[i] < min(pl, vl) || lucky[i + k - 1] > max(pr, vr)) continue;
    minp = (i == 1 ? pl : lucky[i - 1] + 1);
    maxp = lucky[i];
    minv = lucky[i + k - 1];
    maxv = (i == n - k + 1 ? vr : lucky[i + k - 1 + 1] - 1);
    numerator +=
        intersection(minp, maxp, pl, pr) * intersection(minv, maxv, vl, vr);
    minv = (i == 1 ? vl : lucky[i - 1] + 1);
    maxv = lucky[i];
    minp = lucky[i + k - 1];
    maxp = (i == n - k + 1 ? pr : lucky[i + k - 1 + 1] - 1);
    numerator +=
        intersection(minp, maxp, pl, pr) * intersection(minv, maxv, vl, vr);
    if (k == 1 && lucky[i] >= pl && lucky[i] <= pr && lucky[i] >= vl &&
        lucky[i] <= vr)
      --numerator;
  }
  printf("%.15lf\n", (double)numerator / (double)denumerator);
  return 0;
}
