#include <bits/stdc++.h>
#include <map>
using namespace std;

#define MOD 1000000007




int main(){
    int N;
    scanf("%i", &N);

    int p[N+1] = {};
    unordered_map<int, int> m = {};
	
	p[0] = 0;
    for(int i = 0; i < N; i++) {
        char c;
        scanf(" %c", &c);
        int cc = c - 'A';

        p[i+1] = p[i] ^ (1 << cc);
        
        
		if(!m.count(p[i+1]))
			m[p[i+1]] = i+1;
    }
    
    int maxlen = 0;
    for(int i = N; i >= 0; i--) {
        int len = m[p[i]] - i;
        if(len > maxlen) {
			maxlen = len;
		}
		
        for(int j = 0; j < 20; j++) {
			if(!m.count(p[i] ^ (1 << j))) continue;
			
			int len = m[p[i] ^ (1 << j)] - i;
			if(len > maxlen) {
				maxlen = len;
			}
		}
    }
    
    printf("%i\n", maxlen);
    
}