#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define rep(i, a, n) for (int i = (a); i < (n); i++)
#define per(i, a, n) for (int i = (n) - 1; i >= (a); i--)
#define FOR(i, n) rep(i, 0, (n))
#define fi first
#define se second

//char endl = '\n';

int main(void) {
	ios_base::sync_with_stdio(false);
	int n;
	cin >> n;
	string s;
	cin >> s;

	int res = 0;
	vector<int> first((1<<23), n+10);
	int mask = 0;
	first[0] = -1;

	rep(i,0,n) {
		mask ^= (1<<(s[i]-'a'));
		res = max(res, i-first[mask]);
		rep(b,0,20) {
			res = max(res, i-first[mask^(1<<b)]);
		}
		first[mask] = min(first[mask], i);
	}

	cout << res << endl;

	return 0;
}