#include <cstdio>
#include <map>

using namespace std;

int chc(char ch)
{
	return 1 << (ch - 'a');
}

int main()
{
	int N;
	scanf("%d\n", &N);

	int start = -1, koniec = -1, result = 0;
	unsigned int p[N+1], prev =0;
	map<unsigned, int> myMap;
	myMap[0] = 0;

	p[0] = 0;
	for (int i = 1; i <= N; i++)
	{		
		char pivo = getc(stdin);
		int newBeer = chc(pivo);
		// prepocitaj novy stav
		p[i] = prev ^ newBeer;
		prev = p[i];
		// daj do dict-u prvy znamy stav a jeho vyskyt
		if (! myMap.count(p[i])) {
			myMap[p[i]] = i;
		}

		//printf("PI: %d. %d\n", i, p[i]);
	}	

	//pod od konca a hladaj PODOBNY stav
	for (int i = N; i >= result; i--)
	{
		for (char j = 'a'; j <= 't'; j++)
		{
			int pokusnePivo = p[i] ^ chc(j);
			if (myMap.count(pokusnePivo))
			{
				start = myMap[pokusnePivo];
				koniec = i;
				if (result < koniec - start + 1)
				{
					//printf("1 %d %d\n", start, koniec);
					result = koniec - start + 1;
				}
			}
		}

		if (myMap.count(p[i]))
		{
			start = myMap[p[i]];
			koniec = i;
			if (result < koniec - start + 1)
			{
				//printf("2 %d %d\n", start, koniec);
				result = koniec - start + 1;
			}
		}
	}

	printf("%d\n", result == 1 ? result : result-1);

	return 0;
}