#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using ld=double;
#define FOR(i,a,b) for(ll i=a;i<(ll)b;++i)
#define F(n) FOR(i,0,n)
#define FF(n) FOR(j,0,n)
#define aa first
#define bb second
#define PB push_back
#define EQ(a,b) (fabs(a-b)<=(fabs(a+b)*EPS))

int main(){
	ios::sync_with_stdio(0);cout.tie(0);cin.tie(0);
  ll n;
  cin >>n;
  string a;
  cin >> a;
  ll best = 0;
  F(21) {
    map<int,int> early;
    int cur = 0;
    early[cur] = -1;
    FF(n) {
      if (a[j] - 'a' != i) {
        int b = (1 << (a[j] - 'a'));
        cur ^= b;
      }
      if (early.find(cur) != early.end()) best = max(best, j - early[cur]);
      else early[cur] = j;
    }
  }
  cout << best << endl;
	return 0;
}