#include <bits/stdc++.h>
using namespace std;
vector<long long int> lucky;
long long int l, r;
void gen(long long int a) {
  if (a <= 1e11) lucky.push_back(a);
  if (a * 10 + 4 <= 1e11) gen(a * 10 + 4);
  if (a * 10 + 7 <= 1e11) gen(a * 10 + 7);
}
void solve() {
  cin >> l >> r;
  gen(4);
  gen(7);
  sort(lucky.begin(), lucky.end());
  if (l == r) {
    cout << *lower_bound(lucky.begin(), lucky.end(), l);
    return;
  }
  long long int lb = lower_bound(lucky.begin(), lucky.end(), l) - lucky.begin();
  long long int ans = (min(r, lucky[lb]) - l + 1) * lucky[lb], i;
  for (i = lb + 1; lucky[i] <= r; i++) {
    ans += (lucky[i] - lucky[i - 1]) * lucky[i];
  }
  i--;
  if (lucky[i] < r) {
    ans += (r - lucky[i]) * lucky[i + 1];
  }
  cout << ans;
}
int32_t main() {
  ios::sync_with_stdio(false);
  long long int t = 1;
  while (t--) {
    solve();
  }
}
