source_code: import java.util.*;
  
  
  public class Main {
  	private static Scanner in = new Scanner(System.in);
  	public static void main(String args[]){
  		int n = in.nextInt();
  		String s = in.next();
  		if(n==1)
  			System.out.println("1");
  		else{
  			int j=0,i=1,ans=s.length();
  			int h[]=new int[128];
  			h[(int)s.charAt(0)]=1;
  			while(i<n){
  				if(h[(int)s.charAt(i)]==0)
  					ans = i-j+1;
  				h[(int) s.charAt(i)]++;
  				while(j<i && h[(int)s.charAt(j)]>1){
  					h[(int)s.charAt(j)]--;
  					j++;
  					ans = Math.min(ans, i-j+1);
  				}
  				i++;
  			}
  			System.out.println(ans);
  		}
  	}
  }
  