codeforce - lucky sum

#include<bits/stdc++.h>
using namespace std;
#define fast()(ios_base::sync_with_stdio(false),cin.tie(NULL));
#define pb push_back
#define ll long long
#define MAX 4444444445
int main()
{
    fast()
    vector<ll>v;
    v.pb(4);
    v.pb(7);
    for(int i=0;i<v.size();i++)
    {
        if(v[i]*10+4>MAX)break;
        else v.pb(v[i]*10+4);
        if(v[i]*10+7>MAX)break;
        else v.pb(v[i]*10+7);
    }
    ll sum=0,l,r;
    cin>>l>>r;
    while(l<=r)
    {
        ll pos=lower_bound(v.begin(),v.end(),l )- v.begin();
        if(v[pos]>r)sum+=(r-l+1)*v[pos];
        else sum+=(v[pos]-l+1)*v[pos];
        l=v[pos]+1;
    }
    cout<<sum<<endl;
}