#include <bits/stdc++.h>

int getpos(char c)
{
    return 1 << (c - 'a');
}

#define ll long 

using namespace std;

map<ll,int> st;
ll tmp, tmp2;

int main()
{
int res=0;
int n;
cin >> n;
string str;
cin >> str;
tmp = 0;
st.emplace(tmp,-1);



for(int i=0;i<n;i++){

  tmp ^= getpos(str[i]);
  if(st.count(tmp) == 0){
      st.emplace(tmp,i);
  }else{
      res = max(i - st.at(tmp),res);
  }
  for(int j=0;j<20;j++){
      tmp ^= 1<<j;
      if(st.count(tmp)){
        res = max(i-st.at(tmp),res);
      }
      tmp ^= 1<<j;
  }
}
cout<<res<<endl;
return 0;
}