#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second

const int A='t'-'a'+1;
const int N=3e5+9;
int s[1<<A];
int res=0;


int main(){
	ios::sync_with_stdio(0);
	int n;
	cin >> n;
	int m=0;
	s[m]=1;
	for(int i=2; i<=n+1; ++i){
		char c;
		cin>>c;
		m^=(1<<(c-'a'));
		if(!s[m])
			s[m]=i;
		res=max(res, i-s[m]);
		for(int j=0; j<A; ++j)
			if(m){
				if(m&(1<<j))
					if(s[m-(1<<j)])
						res=max(res, i-s[m-(1<<j)]);
			}else{
				if(s[m|(1<<j)])
						res=max(res, i-s[m-(1<<j)]);
			}
	}
	cout<<res<<'\n';
	return 0;
}