#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 50;
const long long mod = 1e9 + 7;
const long long INF = 1e18;
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, 1, 0, -1};
bool compare(const pair<long long, long long>& i,
             const pair<long long, long long>& j) {
  return i.second < j.second;
}
long long fact[N];
vector<bool> is_prime(100000, true);
vector<int> prime;
void pre() {
  fact[0] = 1;
  for (long long i = 1; i < N; i++) {
    fact[i] = i * fact[i - 1];
    fact[i] %= mod;
  }
}
long long modexp(long long x, long long n) {
  long long r = 1;
  while (n) {
    if (n & 1) r = (r * x) % mod;
    x = (x * x) % mod;
    n >>= 1;
  }
  return r % mod;
}
long long modinv(long long x) { return modexp(x, mod - 2); }
long long ncr(long long n, long long r) {
  if (n < r) return 0;
  long long ans =
      (fact[n] % mod * modinv(fact[r]) % mod * modinv(fact[n - r]) % mod) % mod;
  return ans;
}
long long exp(long long x, long long n) {
  long long r = 1;
  while (n) {
    if (n & 1) r = (r * x);
    x = (x * x);
    n >>= 1;
  }
  return r;
}
set<long long> st;
void rec(string s) {
  if (s.size() > 10) return;
  long long num = stoll(s);
  st.insert(num);
  rec(s + "4");
  rec(s + "7");
}
void solve() {
  long long l, r;
  cin >> l >> r;
  rec("4");
  rec("7");
  long long ans = 0;
  for (long long i = l; i <= r; i++) {
    long long next = *(st.lower_bound(i));
    ans += (min(r, next) - i + 1) * next;
    i = next;
  }
  cout << ans << "\n";
  return;
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  for (int i = 0; i < t; i++) {
    solve();
  }
  return 0;
}
