#include <iostream>
#include <string>

using namespace std;

int main()
{
	int n;
	cin >> n;
	string s;
	cin >> s;
	int lets = 't' - 'a' + 1;
	int* prefs = (int*)malloc(sizeof(int) * lets * (n + 1));
	for (int i = 0; i < lets; i++)
	{
		prefs[0 + (n + 1) * i] = 0;
	}
	for (int i = 0; i < n; i++)
	{
		int charnum = s[i] - 'a';
		for (int j = 0; j < lets; j++)
		{
			if (j == charnum)
			{
				prefs[i + 1 + (n + 1) * j] = prefs[i + (n + 1) * j] + 1;
			}
			else
			{
				prefs[i + 1 + (n + 1) * j] = prefs[i + (n + 1) * j];
			}
		}
	}
	int maxlen = 0;
	for (int i = 0; i < n-maxlen; i++)
	{
		for (int j = i + 1; j <= n; j++)
		{
			bool oneoff = false;
			bool fail = false;
			for (int k = 0; k < lets; k++)
			{
				int cou = prefs[j + (n + 1) * k]-prefs[i + (n+1)*k];
				if (cou&1)
				{
					if (oneoff)
					{
						fail = true;
						break;
					}
					else
					{
						oneoff = true;
					}
				}
			}
			if (!fail)
			{
				maxlen=max(maxlen, j-i);
			}
		}
	}
	cout << maxlen << endl;
	return 0;
}