package yukicoder;
import java.util.Scanner;
public class Main{
	public static void main(String[] args)throws Exception{
		new Main().solve();
	}
	boolean check(int kr,int kb,StringBuffer sb){
		for(int i=0;i<sb.length();i++){
			if(sb.charAt(i)=='R'&&i+kr<sb.length()&&sb.charAt(i+kr)=='R'){
				return false;
			}else if(sb.charAt(i)=='B'&&i+kb<sb.length()&&sb.charAt(i+kb)=='B'){
				return false;
			}
		}
		return true;
	}
	void solve(){
		Scanner sc=new Scanner(System.in);
		int kr=sc.nextInt();
		int kb=sc.nextInt();
		String s=sc.next();
		
		int[] block=new int[20];
		int tmp=0;
		for(int i=0;i<30;i++){
			if(s.charAt(i)=='R'||s.charAt(i)=='B'){
				block[tmp]=i;
				tmp++;
			}
		}
		int ans=9999999;
		for(int i=0;i<(1<<21);i++){
			StringBuffer sb=new StringBuffer(s);
			if(ans<=Integer.bitCount(i))continue;
			for(int j=19;j>=0;j--){
				if((1&(i>>j))==1){
					sb=sb.deleteCharAt(block[j]);
				}
			}
//			System.out.println(sb);
			if(check(kr, kb, sb)){
				ans=Math.min(ans,Integer.bitCount(i));
			}
		}
		System.out.println(30-ans);
	}

}