#include <stdio.h>
#include <string>
#include <string.h>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <algorithm>
#define FOR(A, B) for(A=0;A<B;A++)
#define MAXN 111
using namespace std;

long long l,r;
vector<long long> luckies;
void gen(long long x)
{
        if(x <= 15LL*r && x > 0) {
        //printf("%lld\n", x);
                luckies.push_back(x);
        }
        if(x > r) return;
        gen(x*10LL+4LL);
        gen(x*10LL+7LL);
}

int main()
{
        int i,j,k,m;
        int ll,rr;
        scanf("%d %d", &ll, &rr);
        l = (long long)ll; r = (long long)rr;
        gen(0);
        sort(luckies.begin(), luckies.end());
        i = 0;
        while(luckies[i] < l) i++;
        long long ans = (min(luckies[i], r)-l+1)*luckies[i];

        long long prev = luckies[i]+1;
        for(j = i+1; j < luckies.size(); j++) {
                if(prev > r) break;
                ans += (min(luckies[j], r)-prev+1)*(long long)luckies[j];
                prev = luckies[j]+1;
        }
        printf("%I64d\n", ans);
        return 0;
}