#include <bits/stdc++.h>

using namespace std;

const int N = 3e5 + 7;

int n;
char in[N];
int M[1 << 21];

int main(){
	scanf("%d", &n);
	scanf("%s", in + 1);

	for(int i = 0; i < (1 << 20); ++i)
		M[i] = -1;

	int cur = 0;
	M[cur] = 0;

	int ans = 0;
	int dist = 't' - 'a';
	for(int i = 1; i <= n; ++i){
		int bf = i;
		cur ^= 1 << (in[i] - 'a');
		for(int j = 0; j <= dist; ++j)
			if(M[cur ^ (1 << j)] != -1)
				bf = min(bf, M[cur ^ (1 << j)]);
		
		if(M[cur] != -1)
			bf = min(bf, M[cur]);
		else
			M[cur] = i;
		ans = max(ans, i - bf);
	}
	
	printf("%d\n", ans);
	return 0;
}