#include<iostream>
#include<unordered_map>
#include<string>

using namespace std;

int n;
unordered_map<int, int> mp;
int ma = 0;
string s;

int main()
{
	ios::sync_with_stdio(false);
	cin>>n;
	cin>>s;
	int cur = 0;
	mp[0] = -1;
	for(int i = 0; i < n; i++)
	{
		cur ^= 1<<(s[i]-'a');
		if(mp.count(cur))
			ma = max(ma, i-mp[cur]);
		else
			mp[cur] = i;
		for(char c = 'a'; c <= 'z'; c++)
		{
			int cr = cur^(1<<(c-'a'));
			if(mp.count(cr))
					ma = max(ma, i-mp[cr]);
		}
	}
	cout<<ma<<endl;
	return 0;
}