Find The Multiple

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <algorithm>
 4 using namespace std;
 5 typedef long long ll;
 6 int n;
 7 bool flag = false;
 8 void dfs(ll num, int len){
 9     if(len > 19 || flag == 1){
10         return;
11     }
12     if(num % n == 0){
13         flag = true;
14         cout << num << endl;
15         return;
16     }
17     dfs(num * 10, len + 1);
18     dfs(num * 10 + 1, len + 1);
19 }
20 int main(){
21     while(scanf("%d", &n)){
22         if(n == 0)
23             break;
24         flag = false;
25         dfs(1, 1);
26     }
27     
28     return 0;
29 }