import java.util.Arrays;
import java.util.LinkedList;
import java.util.Scanner;

public class Main {
	
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		final int Kr = sc.nextInt();
		final int Kb = sc.nextInt();
		char[] inputs = sc.next().toCharArray();
		
		int min = Integer.MAX_VALUE;
		
		for(int bit = 0; bit < (1 << 20); bit++){
			final int reduced_size = inputs.length - Integer.bitCount(bit);
			char[] reduced_inputs = new char[reduced_size];
			
			for(int normal = 0, reduced = 0, count = 0; normal < inputs.length; normal++){
				if(inputs[normal] == 'W'){
					reduced_inputs[reduced++] = inputs[normal];
					continue;
				}
				
				final boolean is_ignored = (bit & (1 << (count++))) != 0;
				if(is_ignored){
					continue;
				}else{
					reduced_inputs[reduced++] = inputs[normal];
				}
			}
			
			//System.out.println(Arrays.toString(reduced_inputs));
			//sc.next();
			
			boolean ok = true;
			for(int i = 0; i < reduced_size; i++){
				if(reduced_inputs[i] == 'R'
						&& ((i - Kr >= 0 && reduced_inputs[i - Kr] == 'R')
								|| (i + Kr < reduced_size && reduced_inputs[i + Kr] == 'R'))){
					ok = false;
					break;
				}else if(reduced_inputs[i] == 'B'
						&& ((i - Kb >= 0 && reduced_inputs[i - Kb] == 'B')
								|| (i + Kb < reduced_size && reduced_inputs[i + Kb] == 'B'))){
					ok = false;
					break;
				}
			}
			
			if(ok){
				min = Math.min(min, Integer.bitCount(bit));
			}
		}
		
		System.out.println(inputs.length - min);
	}
	
}