#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define MAXK 64
#define ALFA 26
#define HASH 102400
#define MAXL 102400

static size_t cbuf[MAXK][ALFA];

struct ch
{
  size_t hash;
  unsigned char val[ALFA];
  struct ch *next;
};

static struct ch chars[MAXL];

struct hte
{
  struct ch *list;
  unsigned gen;
};

static struct hte table[HASH];
static unsigned gen;

static size_t
hash_fn (const struct ch *ch)
{
  size_t val, i;

  val = 0;
  for (i = 0; i < ALFA; i++)
    val = (val >> 31) ^ (val << 1) ^ ch->val[i];
  return val;
}

static void
hash_clear (void)
{
  gen++;
}

static int
hash_add (struct ch *ch)
{
  struct ch *ht;
  struct hte *hte;

  ch->hash = hash_fn (ch);
  hte = table + ch->hash % HASH;
  if (hte->gen != gen)
    {
      hte->gen = gen;
      hte->list = NULL;
    }
  for (ht = hte->list; ht != NULL; ht = ht->next)
    {
      if (ht->hash == ch->hash
	  && memcmp (ht->val, ch->val, sizeof (ht->val)) == 0)
	return 1;
    }
  ch->next = hte->list;
  hte->list = ch;
  return 0;
}

int
main (void)
{
  for (;;)
    {
      static char orig[MAXL], clean[MAXL];
      char *p, *q;
      unsigned k;
      size_t i;
      int c;

      scanf("%u", &k);
      while ((c = getchar ()) != '\n')
	;
      if (k == 0)
	break;
      hash_clear ();
      gets(orig);
      q = clean;
      for (p = orig; *p != 0; p++)
	{
	  if (*p >= 'a' && *p <= 'z')
	    *q++ = *p;
	  else if (*p >= 'A' && *p <= 'Z')
	    *q++ = *p - ('A' - 'a');
	}
      *q = 0;
      for (i = 0; i < ALFA; i++)
	cbuf[0][i] = 0;
      for (i = 0; clean[i] != 0; i++)
	{
	  size_t old, new;

	  old = i % MAXK;
	  new = (i + 1) % MAXK;
	  memcpy (cbuf[new], cbuf[old], sizeof (cbuf[new]));
	  cbuf[new][clean[i] - 'a']++;
	  if (i + 1 >= k)
	    {
	      struct ch *ch;
	      unsigned char j;

	      old = (i + 1 - k) % MAXK;
	      ch = chars + i;
	      for (j = 0; j < ALFA; j++)
		ch->val[j] = cbuf[new][j] - cbuf[old][j];
	      if (hash_add (ch) != 0)
		break;
	    }
	}
      q = clean;
      for (p = orig; *p != 0; p++)
	{
	  if ((*p >= 'a' && *p <= 'z')
	      || (*p >= 'A' && *p <= 'Z'))
	    {
	      if (q == clean + i)
		break;
	      q++;
	    }
	}
      printf ("%u\n", p - orig);
    }
  return 0;
}