source_code: import java.io.BufferedReader;
  import java.io.FileReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.util.ArrayList;
  import java.util.StringTokenizer;
  
  public class Round364C {
  	public static void main(String[] args) throws NumberFormatException, IOException {
  		Scanner sc = new Scanner(System.in);
  		n = sc.nextInt();
  		k = 0;
  		
  		String line = sc.nextLine();
  		
  		ArrayList<Character> poks = new ArrayList<Character>();
  		boolean ex[] = new boolean[256];
  		
  		for(int i=0; i<n; i++)
  		{
  			if(!ex[line.charAt(i)])
  			{
  				ex[line.charAt(i)] = true;
  				poks.add(line.charAt(i));
  			}
  		}
  		
  		
  		int l = 0;
  		int r = 0;
  		int dist = 1;
  		int occ[] = new int[256];
  		occ[line.charAt(0)] = 1;
  		
  		int min = n;
  		while(r < n)
  		{
  			if(dist == poks.size())
  				min = Math.min(min, r - l + 1);
  			if(l < r && dist == poks.size())
  			{
  				
  				occ[line.charAt(l)]--;
  				if(occ[line.charAt(l)] == 0)
  					dist--;
  				l++;
  				continue;
  			}
  			if(r < n-1){
  				occ[line.charAt(r+1)]++;
  				if(occ[line.charAt(r+1)] == 1)
  					dist++;
  			}
  			r++;
  		}
  		System.out.println(min);
  		
  	}
  	
  	static int n,k;
  	static int dp[][][];
  	
  	static class Scanner {
  		BufferedReader br;
  		StringTokenizer st;
  
  		Scanner(FileReader f) {
  			br = new BufferedReader(f);
  		}
  
  		public boolean ready() throws IOException {
  			return br.ready();
  		}
  
  		Scanner(InputStream s) {
  			br = new BufferedReader(new InputStreamReader(s));
  		}
  
  		String next() throws IOException {
  			while (st == null || !st.hasMoreTokens())
  				st = new StringTokenizer(br.readLine());
  			return st.nextToken();
  		}
  
  		String nextLine() throws IOException {
  			return br.readLine();
  		}
  
  		int nextInt() throws NumberFormatException, IOException {
  			return Integer.parseInt(next());
  		}
  
  		long nextLong() throws NumberFormatException, IOException {
  			return Long.parseLong(next());
  		}
  	}
  }
  