Find The Multiple

Description
Given a positive integer n, write a program to find out a nonzero multiple m of n whose decimal representation contains only the digits 0 and 1. You may assume that n is not greater than 200 and there is a corresponding m containing no more than 100 decimal digits.
Input
The input file may contain multiple test cases. Each line contains a value of n (1 <= n <= 200). A line containing a zero terminates the input.
Output
For each value of n in the input print a line containing the corresponding value of m. The decimal representation of m must not contain more than 100 digits. If there are multiple solutions for a given value of n, any one of them is acceptable.
Sample Input
2
6
19
0
Sample Output
10
100100100100100100

111111111111111111

#include<cstdio>#include<iostream>#include<algorithm>using namespace std;bool f;void dfs(__int64 x,int n,int k){    if(f||k==19) return;    if(x%n==0)    {        f=true;        printf("%I64d\n",x);        return;    }    dfs(x*10,n,k+1);    dfs(x*10+1,n,k+1);}int main(){    int n;    while(cin >> n)    {        f=false;        if(n==0) return 0;        dfs(1,n,0);    }    return 0;}