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

char s[100010];
int x[26];
char h[400000][27];

int al(char z)
{
	return (z>='A' && z<='Z') ;
}

char a[26];

int main()
{
	int k,i,j,p,l,mo,m;
	srand(123437);
	for (i=0;i<26;i++) x[i]=(97+rand()+rand()+rand()+rand());
	while (1)
	{
		scanf("%d\n",&k);
		if (k==0) break;
		i=0;
		while(1)
		{
			scanf("%c",s+i);
			if (s[i]=='\n') break;
		}
		s[i]=0;
		mo=strlen(s)*4+105;
		if (mo>400000-3) mo=400000-3;
		for (i=0;i<mo;i++) h[i][0]=0;
		for (i=0;s[i];i++) if (s[i]>='a' && s[i]<='z') s[i]-=-'A'+'a';
		i=0;j=0;
		while (s[i] && (!al(s[i]))) i++;
		if (s[i]==0) { printf("%d\n",i); continue; }
		j=i;
		p=0;
		l=0;
		for (m=0;m<26;m++) a[m]=0;
		while (s[j] && p<k)
		{
			if (s[j] && al(s[j])) 
			{
				a[s[j]-'A']++;
				l+=x[s[j]-'A'];
				p++;
			}
			j++;
		}
		if (p<k) { printf("%d\n",j); continue; }
		while (s[j])
		{
			p=l%mo;
			while (h[p][0])
			{
				for (m=0;m<26;m++) if (a[m]!=h[p][m+1]) break;
				if (m>=26) { l=-1; break; }			
				p=(p+1)%mo;
			}
			if (l==-1) break;			
			p=l%mo;
			while (h[p][0]) p=(p+1)%mo;
			h[p][0]=1;
			for (m=0;m<26;m++) h[p][m+1]=a[m];
			l-=x[s[i]-'A'];
			a[s[i]-'A']--;
			i++;
			while (s[i] && !al(s[i])) i++;
			while (s[j] && !al(s[j])) j++;
			if (s[j]) { 
			a[s[j]-'A']++;
			l+=x[s[j]-'A']; j++; 
			}
		}	
		if (!(s[j]))
		{
			p=l%mo;
			while (h[p][0])
			{
				for (m=0;m<26;m++) if (a[m]!=h[p][m+1]) break;
				if (m>=26) { l=-1; break; }			
				p=(p+1)%mo;
			}
		}
		if (l==-1) j--;
		printf("%d\n",j);
	}
	return 0;
}