#include <stdio.h>
#define N 3

char cs[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
// char cs[] = "abAB01";
char s[N + 1];
int sz = sizeof(cs) / sizeof(char) - 1;

void func(int n)
{
  int i;
  for (i = 0; i < sz; ++i) {
    s[N - n - 1] = cs[i];
    if (n == 0)printf("%s\n", s);
    else func(n - 1);
  }
}

int main()
{
  s[N] = '\0';
  func(N - 1);
  return 0;
}