/*
You are given a string consisting of lower and upper case characters.
You need to find the length of the longest palindrome which you can create by using the characters from the string.
Note: Upper case and lower case characters are different from each other i.e, "Aa" is not a palindrome as 'A' != 'a'.

Input format
There are 2 lines of input

First line contains the size of the string

Second line contains the string.

Output format
Print the length of the longest palindrome possible.

Sample Input 1
4 bbde

Sample Output 1
3

Explanation
The possible 3 size palindrome strings are :- beb and bdb

Constraints
1 <= Size of String <= 10^4
*/

function getIndex(char){
  return Math.floor(char.charCodeAt(0));
}

/**
 * @param {number} n
 * @param {string} s
 * @return {number}
 */
// solve simply by using hashing : hash[256] for all characters
function longestPalindrome(n, str) {
    let hash=new Array(256).fill(0);
    let ans=0;
   for(let i=0;i<n;i++){
       hash[getIndex(str[i])]++;
   }
    for(let i=0;i<256;i++){
        if(hash[i]&1==1)
        {
            ans+=Math.floor(hash[i]-1);
            hash[i]=1;
        }
        else{
            ans+=hash[i];
            hash[i]=0;
        }
    }

    for(let i=0;i<256;i++){
        if(hash[i]==1){
            ans++;
            break;
        }
    }
    return ans;


}

function main() {
    const n = parseInt(readLine())
    const str = readLine()
    const result = longestPalindrome(n, str)
    console.log(result)
}