#include <bits/stdc++.h>
#define FOR(i, n) for(int i = 0; i < (n); ++i)
#define REP(i, a, b) for(int i = (a); i < (b); ++i)
#define TRAV(i, a) for(auto & i : (a))
#define SZ(x) ((int)(x).size())
#define X first
#define Y second
#define MP std::make_pair
#define PR std::pair
typedef long long ll;
typedef std::pair<int, int> PII;
typedef std::vector<int> VI;

const int N = 300005;

int pos[N];
int where[1<<20];
int main(){
	std::ios_base::sync_with_stdio(false);
	std::cin.tie(0);
	int n;
	std::cin >> n;
	VI A(n);
	FOR(i, n){
		char x;
		std::cin >> x;
		A[i] = x-'a';
	}
	int mask = 0;
	pos[0] = mask;
	REP(i, 1, n+1){
		mask = mask ^ (1<<A[i-1]);
		pos[i] = mask;
		where[mask] = i;
	}
	int ans = 0;
	FOR(i, n+1){
		int best = where[pos[i]]-i;
		FOR(b, 20){
			int ms = pos[i]^(1<<b);
			best = std::max(best, where[ms]-i);
		}
		ans = std::max(ans, best);
	}
	std::cout << ans << "\n";
	return 0;
}