#include<bits/stdc++.h>
using namespace std;
using ll = long long;

#define D if(0)

const int NMAX = 312345;
const int abclen = 't'-'a'+2;

int fpoz [1<<abclen];

char in [NMAX];
int main()
{
	int n;
	scanf("%d%s",&n,in);
	for(int i=0;i<(1<<abclen);i++) fpoz[i]=-1;
	int prefix=0;
	int out=0;
	for(int i=0;i<n;i++)
	{
		if(fpoz[prefix] == -1) fpoz[prefix]=i;
		prefix ^= (1<<int(in[i]-'a'));
		if(fpoz[prefix]!=-1) out = max(out,i-fpoz[prefix]);
		for(int j=0;j<abclen;j++)
		{
			int modprefix = prefix ^ (1<<j);
			if(fpoz[modprefix]!=-1) out = max(out,i-fpoz[modprefix]);
		}
	}
	printf("%d\n",out+1);
	return 0;
}