source_code: import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Map;
  import java.util.Scanner;
  import java.util.Set;
  
  /**
   * @author grozhd
   */
  public class P3 {
  
      public static void main(String[] args) {
          Scanner sc = new Scanner(System.in);
  
          int n = sc.nextInt();
  
          String s = "";
          while (s.length() == 0) {
              s = sc.nextLine();
          }
          char[] pokemons = s.toCharArray();
  
          Set<Character> pokemonTypes = new HashSet<>();
          for (int i = 0; i < n; i++) {
              pokemonTypes.add(pokemons[i]);
          }
  
          int types = pokemonTypes.size();
  
          int l = 0;
          int r = 0;
          int min = n;
          Map<Character, Integer> currentPokemons = new HashMap<>();
  
  
          while (r < n) {
              while (currentPokemons.size() < types && r < n) {
                  char pokemon = pokemons[r++];
                  currentPokemons.merge(pokemon, 1, (a, b) -> a + b);
              }
              min = Math.min(r - l, min);
  
              while (currentPokemons.size() == types) {
                  char pokemon = pokemons[l++];
                  if (currentPokemons.get(pokemon) == 1) {
                      currentPokemons.remove(pokemon);
                  } else {
                      min = Math.min(r - l, min);
                      currentPokemons.put(pokemon, currentPokemons.get(pokemon) - 1);
                  }
              }
          }
  
          min = Math.min(min, r - l + 1);
          min = Math.max(min, types);
  
          System.out.println(min);
  
      }
  }