source_code: import java.util.*;
  
  public class helloWorld 
  {
  	public static void main(String[] args) 
  	{		
  		Scanner in = new Scanner(System.in);
  		int n = in.nextInt();
  		int m = in.nextInt();
  		int[] ar = new int[200];
  		
  		String str = in.next();
  		for(int i = 0; i < str.length(); i++)
  			ar[ str.charAt(i) ]++;
  			
  		int ans = 100000;
  		
  		for(int i = 'A'; i < 'A' + m; i++)
  			ans = Math.min(ans, ar[i]);
  		ans *= m;
  		
  		System.out.println(ans);
  		
  		in.close();
  	}
  }
  
  