source_code: import java.io.*;
  import java.util.*;
  import java.text.*;
  import java.math.*;
  
  public class main {
      public static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      public static PrintWriter pw = new PrintWriter(System.out);
      public static String line;
      public static StringTokenizer st;
      public static ArrayList<ArrayList<Integer>> adjList;
      public static int[] dr = {-1, 0, 1, 0, -1, 1, 1, -1};
      public static int[] dc = {0, 1, 0, -1, 1, 1, -1, -1};
  
      public static void main(String[] args) throws Exception{
          int N = Integer.parseInt(br.readLine());
          char[] A = br.readLine().toCharArray();
  
          HashSet<Character> cndD = new HashSet<Character>();
          for(int i = 0; i < N; i++){
              cndD.add(A[i]);
          }
  
          int cnt = cndD.size();
  
          int a = 0;
          int b = 0;
  
          int ans = (1 << 30);
          HashMap<Character, Integer> d = new HashMap<Character, Integer>();
          while(b < N){
              if(d.containsKey(A[b])){
                  if(A[a] == A[b]){
                      a++;
                      while(d.get(A[a]) > 1){
                          d.put(A[a], d.get(A[a])-1);
                          a++;
                      }
                  } else{
                      d.put(A[b], d.get(A[b])+1);
                  }
              } else{
                  d.put(A[b], 1);
              }
              if(d.size() == cnt){
                  ans = Math.min(b-a+1, ans);
              }
              b++;
          }
  
          pw.print(ans + "\n");
          pw.close();
          br.close();
      }
  }
  
  class Pair implements Comparable<Pair>{
      public int a, b;
  
      Pair(int a, int b){
          this.a = a;
          this.b = b;
      }
  
      @Override
      public int compareTo(Pair P){
          if(P.b != this.b){
              return b - P.b;
          } else if(P.a == this.a){
              return a - P.a;
          } else{
              return 0;
          }
      }
  
      public String toString(){
          return a + " " + b;
      }
  }
  