import java.io.IOException;
import java.util.InputMismatchException;

public class Main {
	int r, b;
	char[] c;
	int ans;

	void backtrack(int k, boolean[] use, int cnt) {
		if (ans <= cnt) {
			return;
		}
		if (20 <= k) {
			if (check(use)) {
				ans = cnt;
			}
		} else {
			use[k] = true;
			backtrack(k + 1, use, cnt + 1);
			use[k] = false;
			backtrack(k + 1, use, cnt);
		}
	}

	boolean check(boolean[] use) {
		StringBuilder tmp = new StringBuilder("");
		int id = 0;
		for (int i = 0; i < 30; i++) {
			if (c[i] == 'W') {
				tmp = tmp.append(c[i]);
			} else {
				if (!use[id]) {
					tmp = tmp.append(c[i]);
				}
				id++;
			}
		}

		char[] nc = tmp.toString().toCharArray();
		int n = nc.length;
		for (int i = 0; i < n; i++) {
			if (nc[i] == 'R') {
				if (0 <= i - r && nc[i - r] == 'R') {
					return false;
				}
				if (i + r < n && nc[i + r] == 'R') {
					return false;
				}
			} else if (nc[i] == 'B') {
				if (0 <= i - b && nc[i - b] == 'B') {
					return false;
				}
				if (i + b < n && nc[i + b] == 'B') {
					return false;
				}
			}
		}
		return true;
	}

	void run() {
		MyScanner sc = new MyScanner();

		r = sc.nextInt();
		b = sc.nextInt();
		c = sc.next().toCharArray();
		ans = 30;

		backtrack(0, new boolean[20], 0);
		System.out.println(30-ans);
	}

	public static void main(String[] args) {
		new Main().run();
	}

	public void mapDebug(int[][] a) {
		System.out.println("--------map display---------");
		for (int i = 0; i < a.length; i++) {
			for (int j = 0; j < a[i].length; j++) {
				System.out.printf("%3d ", a[i][j]);
			}
			System.out.println();
		}
		System.out.println("----------------------------" + '\n');
	}

	class MyScanner {
		int read() {
			try {
				return System.in.read();
			} catch (IOException e) {
				throw new InputMismatchException();
			}
		}

		boolean isSpaceChar(int c) {
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}

		boolean isEndline(int c) {
			return c == '\n' || c == '\r' || c == -1;
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		int[] nextIntArray(int n) {
			int[] array = new int[n];
			for (int i = 0; i < n; i++)
				array[i] = nextInt();
			return array;
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		long[] nextLongArray(int n) {
			long[] array = new long[n];
			for (int i = 0; i < n; i++)
				array[i] = nextLong();
			return array;
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		double[] nextDoubleArray(int n) {
			double[] array = new double[n];
			for (int i = 0; i < n; i++)
				array[i] = nextDouble();
			return array;
		}

		String next() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isSpaceChar(c));
			return res.toString();
		}

		String[] nextStringArray(int n) {
			String[] array = new String[n];
			for (int i = 0; i < n; i++)
				array[i] = next();

			return array;
		}

		String nextLine() {
			int c = read();
			while (isEndline(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isEndline(c));
			return res.toString();
		}
	}
}