#include <bits/stdc++.h>
using namespace std;
using namespace std;
template <class T>
void setmax(T &a, T b) {
  if (a < b) a = b;
}
template <class T>
void setmin(T &a, T b) {
  if (b < a) a = b;
}
template <class T>
T Abs(T x) {
  return x > 0 ? x : -x;
}
template <class T>
inline T sqr(T x) {
  return x * x;
}
template <class T>
inline bool isPrime(T n) {
  if (n <= 1) return false;
  for (T i = 2; i * i <= n; i++)
    if (n % i == 0) return false;
  return true;
}
template <class T>
string toString(T n) {
  ostringstream oss;
  oss << n;
  oss.flush();
  return oss.str();
}
int toInt(string s) {
  int r = 0;
  istringstream sin(s);
  sin >> r;
  return r;
}
long long toLl(string s) {
  long long r = 0;
  istringstream sin(s);
  sin >> r;
  return r;
}
double toDouble(string s) {
  double r = 0;
  istringstream sin(s);
  sin >> r;
  return r;
}
bool IsVowel(char ch) {
  ch = tolower(ch);
  if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u')
    return true;
  return false;
}
bool isUpperCase(char c) { return c >= 'A' && c <= 'Z'; }
bool isLowerCase(char c) { return c >= 'a' && c <= 'z'; }
long long Pow(long long B, long long P) {
  long long R = 1;
  while (P > 0) {
    if (P % 2 == 1) R = (R * B);
    P /= 2;
    B = (B * B);
  }
  return R;
}
int BigMod(long long B, long long P, long long M) {
  long long R = 1;
  while (P > 0) {
    if (P % 2 == 1) {
      R = (R * B) % M;
    }
    P /= 2;
    B = (B * B) % M;
  }
  return (int)R;
}
long long mulmod(long long a, long long b, long long c) {
  long long x = 0, y = a % c;
  while (b > 0) {
    if (b % 2 == 1) {
      x = (x + y) % c;
    }
    y = (y * 2) % c;
    b /= 2;
  }
  return x % c;
}
void ASCII_Chart() {
  int i, j, k;
  printf("ASCII Chart:(30-129)\n");
  for (i = 30; i < 50; i++) {
    for (j = 0; j < 5; j++) {
      k = i + j * 20;
      printf("%3d---> '%c'   ", k, k);
    }
    printf("\n");
  }
}
double deg2rad(double x) { return (3.141592653589793 * x) / 180.0; }
double rad2deg(double x) { return (180.0 * x) / 3.141592653589793; }
typedef struct {
  long long a, b;
} Ind;
map<string, long long> mp;
long long test, sum, ans, n, i, j, k, m, cnt, siz, fl, rw, cl;
vector<long long> ar;
string str;
void rec(long long n, long long l) {
  if (l > 10) return;
  if (n) ar.push_back(n);
  rec(n * 10 + 4, l + 1);
  rec(n * 10 + 7, l + 1);
  return;
}
vector<long long> arr;
int main() {
  ios_base::sync_with_stdio(false);
  rec(0, 0);
  long long l, r;
  cin >> l >> r;
  sort(ar.begin(), ar.end());
  for (i = 0; i < ar.size(); i++) {
    if (ar[i] >= l) arr.push_back(ar[i]);
    if (ar[i] >= r) break;
  }
  long long pre = l;
  for (i = 0; i < arr.size(); i++) {
    sum += arr[i] * (min(arr[i], r) - pre + 1);
    pre = arr[i] + 1;
  }
  cout << sum << endl;
  return 0;
}
