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

int main(){
	int N;
	cin >> N;
	
	char c[N];
	int pref[N + 1];
	pref[0] = 0;
	
	for(int i = 0; i<N; i++){
		cin >> c[i];
		pref[i + 1] = pref[i] ^ (1 << (c[i] -'a'));
	}
	
	int last[2000000];
	fill (last, last + 2000000, 1e9);
	last[0] = 0;
	
	int ans = 0;
	for(int i = 0; i<=N; i++){
		for(int j = 0; j<20; j++){
			last[pref[i] ^ (1 << j)] = i;
		}
		
		last[pref[i]] = i;
	}
	
	for (int i = 0; i <= N; i++) {
		ans = max (ans, last[pref[i]] - i);
	}
	
	cout << ans;	
}