#include <bits/stdc++.h>
using namespace std;
using ll = long long int;
using ld = long double;
using pi = pair<int, int>;
const double PI = acos(-1.0);
const double eps = 1e-9;
const ll mod = 1e9 + 7;
const int inf = 1e7;
const int MAXN = 1e5 + 5;
vector<ll> lucky;
void gen(ll num) {
  if (num > 2e9) return;
  if (num > 0) lucky.push_back(num);
  gen(num * 10 + 4);
  gen(num * 10 + 7);
}
void cp() {
  ll pL, pR, vL, vR;
  int k;
  cin >> pL >> pR >> vL >> vR >> k;
  gen(0);
  sort(lucky.begin(), lucky.end());
  ll total = 0;
  for (int i = 0; i + k - 1 < ((int)lucky.size()); i++) {
    bool over = true;
    ll L = pL;
    if (i) L = max(L, lucky[i - 1] + 1);
    ll R = min(pR, lucky[i]);
    over &= R == lucky[i];
    ll dL = max(0LL, R - L + 1);
    L = max(vL, lucky[i + k - 1]);
    R = vR;
    if (i + k < ((int)lucky.size())) R = min(R, lucky[i + k] - 1);
    over &= L == lucky[i];
    ll dR = max(0LL, R - L + 1);
    total += dL * dR;
    L = vL;
    if (i) L = max(L, lucky[i - 1] + 1);
    R = min(vR, lucky[i]);
    over &= R == lucky[i];
    dL = max(0LL, R - L + 1);
    L = max(pL, lucky[i + k - 1]);
    R = pR;
    if (i + k < ((int)lucky.size())) R = min(R, lucky[i + k] - 1);
    over &= L == lucky[i];
    dR = max(0LL, R - L + 1);
    total += dL * dR - over;
  }
  ld ans = ld(total) / ld(pR - pL + 1) / ld(vR - vL + 1);
  cout << setprecision(20) << fixed;
  ;
  cout << ans << '\n';
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  int t;
  t = 1;
  while (t--) {
    cp();
  }
  return 0;
}
