#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")
using namespace std;
const int INF = (int)1e9;
const int EPS = 1e-6;
const int mod = 1000000007;
const long double PI = 3.14159265359;
const int dx4[4] = {0, 1, 0, -1};
const int dy4[4] = {-1, 0, 1, 0};
const int dx8[8] = {-1, -1, -1, 0, 1, 1, 1, 0};
const int dy8[8] = {-1, 0, 1, 1, 1, 0, -1, -1};
inline bool grid_inside(int x, int y, int n, int m) {
  return x >= 1 && x <= n && y >= 1 && y <= m;
}
template <typename T>
T lcm(T a, T b) {
  return (a * b) / __gcd(a, b);
}
template <typename T>
T Dis(T x1, T y1, T x2, T y2) {
  return sqrt(((x1 - x2) * (x1 - x2)) + ((y1 - y2) * (y1 - y2)));
}
template <typename T>
T Angle(T x1, T y1, T x2, T y2) {
  return atan((double)(y1 - y2) / (double)(x1 - x2));
}
inline int Set(int N, int pos) { return N = N | (1 << pos); }
inline int Reset(int N, int pos) { return N = N & ~(1 << pos); }
inline bool Check(int N, int pos) { return (bool)(N & (1 << pos)); }
template <class T, class X>
inline T togglebit(T a, X i) {
  T t = 1;
  return (a ^ (t << i));
}
bool compare(const pair<int, int>& i, const pair<int, int>& j) {
  return i.first < j.first;
}
int LSOne(long long int n) { return log2(n & -n) + 1; }
int rangeClear(int n, int i, int j) {
  int ones = ~0;
  int a = ones << (j + 1);
  int b = (i << 2) - 1;
  int mask = a | b;
  int ans = n & mask;
  return ans;
}
long long int mul_mod(long long int x, long long int y, long long int mod) {
  long long int i = 0, j = x;
  while (y > 0) {
    if (y & 1) {
      i = (i + j) % mod;
    }
    j = (j + j) % mod;
    y >>= 1;
  }
  return i;
}
long long int fast_power(long long int a, int x) {
  if (x == 0)
    return 1;
  else if (x == 1)
    return a;
  else {
    long long int R = fast_power(a, x >> 1);
    if (!(x & 1))
      return R * R;
    else
      return R * a * R;
  }
}
long long int fast_power_unlocked(long long int a, long long int n,
                                  long long int mod) {
  long long int res = 1;
  while (n > 0) {
    if (n & 1) {
      res = mul_mod(res, a, mod);
    }
    a = mul_mod(a, a, mod);
    n = n >> 1;
  }
  return res;
}
long long int modInverse(long long int A, long long int M) {
  return fast_power_unlocked(A, M - 2, M);
}
const int maxn = 1000;
void solve() {
  long long int l, r;
  cin >> l >> r;
  vector<long long int> v;
  long long int ans = 0;
  for (int i = 1; i <= 9; i++) {
    int mask = (1 << i);
    for (int j = 0; j < mask; j++) {
      bitset<9> b(j);
      string s = "";
      if (j == 0) {
        for (int k = 0; k < i; k++) {
          s += "4";
        }
      } else {
        for (int k = i - 1; k >= 0; k--) {
          s += (b[k]) ? "7" : "4";
        }
      }
      v.emplace_back(stoll(s));
    }
  }
  v.emplace_back(4444444444);
  int sz = v.size();
  for (int i = 0; i < sz; i++) {
    if (v[i] >= l) {
      if (v[i] >= r) {
        ans += ((r - l + 1) * v[i]);
        break;
      }
      ans += (v[i] - l + 1) * v[i];
      l = v[i] + 1;
    }
  }
  cout << ans;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  ;
  for (auto blockTime = make_pair(chrono::high_resolution_clock::now(), true);
       blockTime.second;
       fprintf(stderr, "%s: %ld ms\n", "Time Taken",
               chrono::duration_cast<chrono::milliseconds>(
                   chrono::high_resolution_clock::now() - blockTime.first)
                   .count()),
            fflush(stderr), blockTime.second = false) {
    solve();
  }
}
