#include<iostream>
#include<string>
#include<vector>
using namespace std;

uint32_t count_bits(uint32_t bits) {
    uint32_t count = 0;
    for (uint8_t shift = 0; shift < 32; shift++) {
        count += ((bits & (1 << shift)) == 0) ? 0 : 1;
    }
    return count;
}

int main() {
    int n;
    cin >> n;
    vector<uint32_t> amounts(n+1);
    amounts[0] = 0;

    string days;
    cin >> days;

   

    uint32_t cur = 0;
    for(uint32_t i = 0; i < n; i++){
        cur ^= (1 << (days[i]-'a'));
        amounts[i+1] = cur;
    }

    if (count_bits(cur) <= 1) {
        cout << n << endl;
        return 0;
    }

    for (uint32_t len = n-1; len >= 0; len--) {
        for (uint32_t offset = 0; offset < (n - len); offset++) {
            if (count_bits(amounts[len+offset] ^ amounts[offset]) <= 1) {
                cout << len << endl;
                return 0;
            }
        }
    }

    return 1;
}