POJ 1426 Find The Multiple dfs

輸出結果有點不能理解

#include <algorithm>
#include <iostream>
#include <stdio.h>
#include <queue>
#include <string.h>
using namespace std;
int n;
int flag;

void dfs(unsigned long long a, int k)//unsigned long long的最大值：18446744073709551615
{
    if(flag||k==19)    return ;
    if(a%n==0){
        printf("%I64u\n", a);
        flag = 1;
        return;
    }else {
        dfs(a*10,k+1);
        dfs(a*10+1,k+1);
    }
}
int main()
{
    while(~scanf("%d", &n)){
        if(n == 0)  break;
        flag = 0;
        dfs(1,0);
    }

    return 0;
}