#include <iostream>
#include <vector>
#include <string>
#include <array>


using namespace std;

int main()
{

	int n;
	while (cin >> n) {
		string in;
		cin >> in;


		int l=0;
		int s=0;

		array<int,32> c;
		c.fill(0);
		
		int x,y;
		int max = 0;
		for (int i=0; i<in.size(); ++i) {
			c.fill(0);
			l=0;
			s=in.size();

			for (int j=i; j<in.size(); ++j) {
				c[in[j]-'a']++;
				if (c[in[j]-'a']%2==0) {
					s++;
					l--;
			        } else {
					s--;
					l++;
				}

				if (l<=1 && (j-i) > max) {
					max = j-i;
				}
			}
		}

		cout << max+1 << endl;

	}

	return 0;
}