#include <stdio.h>
#include <string>
#include <iostream>

using namespace std;

int bitCount(int i) {
        i = i - ((i >> 1) & 0x55555555);
        i = (i & 0x33333333) + ((i >> 2) & 0x33333333);
        i = (i + (i >> 4)) & 0x0f0f0f0f;
        i = i + (i >> 8);
        i = i + (i >> 16);
        return i & 0x3f;
//    return 1;
}

int main() {
    int L;
    scanf("%d", &L);

    string line;
    cin >> line;
    int map[L];
    int right[L];
    for (int i = 0; i < L; i++) {
        map[i] = line[i] - 'a';
        // cout << map[i] << endl;
    }

    right[L-1] = map[L-1];
    for (int i = L-2; i >= 0; i--) {
        right[i] = right[i+1] ^ map[i];
    }

    for (int length = L; length >= 0; length--) {
            if (length != L && length%2 == 0) {
                continue;
            }
            int minBitCount = 9999999;
            for (int j = 0; j < L-length+1; j++) {
                int diff;
                if (j < L-length) {
                    diff = right[j+length] ^ right[j];
                }
                else {
                    diff = right[j];
                }

//                System.out.printf("%d:%d - %s\n", i,j,Integer.toString(diff, 2));
                int bc = bitCount(diff);
                if (bc <= 1) {
                    cout << length << endl;
                    return 0;
                }
                if (bc < minBitCount) {
                    minBitCount = bc;
                }
            }

            if (minBitCount > 2) {
                length -= (minBitCount-2);
            }
        }


    return 0;
}