#include <string>
#include <cstdio>
#include <cassert>
#include <cstring>
#include <algorithm>

using namespace std;

#define dbg(...) fprintf(stderr, __VA_ARGS__)

int l, r, n, nw, st, fi;
long long w[100005];

int len(int k)
{
        int res = 0;
        while (k) ++res, k /= 10;
        return res;
}

void gen(int i, long long num)
{
        w[nw++] = num;

        if (i == n)
                return ;

        gen(i+1, num*10+4);
        gen(i+1, num*10+7);
}

int main()
{
#ifndef ONLINE_JUDGE
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
#endif

        scanf("%d %d", &l, &r);
        n = len(r)+1;

        nw = 2;
        w[0] = 4, w[1] = 7;
        gen(1, 4);
        gen(1, 7);

        sort(w, w+nw);
        long long sum = 0, k = l;
        bool ok = 0;

        for (int i = 0; i < nw; ++i)
                if (k <= w[i] && k <= r)
                {
                        sum += (min(w[i], (long long)r)-k+1)*w[i];
//                      dbg("%I64d %I64d %I64d\n", k, w[i], w[i]-k+1);
                        k = w[i]+1;
                        ok = 1;
                }

        printf("%I64d", sum);

        return 0;
}