lucky numbers

#include<bits/stdc++.h>

using namespace std;

int main(){

    ios_base::sync_with_stdio(false);
    cin.tie();

    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

    int a, b; cin >> a >> b;
    bool found = false;
    for(int i = a; i <= b; i++){
        bool is_lucky = true;

        int x = i;
        while(x){
            int curr_digit = x % 10;
            if(curr_digit != 7 and curr_digit != 4)
                is_lucky = false;
            x /= 10;
        }
        if(is_lucky){
            found = true;
            cout << i << ' ';
        }
    }
    if(not found)
        cout << -1;

    return 0;
}