#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>
#include <string>

using namespace std;

const int N = 30;
int kr, kb;
string s;

int check(int bits) {
	string str(60, '?');
	int nw = 0;
	int nrb = 0;

	for (int i = 0; i < N; i++) {
		if (s[i] == 'W') {
			str[nw + nrb] = 'W';
			nw++;
		} else if ((bits >> (i - nw)) & 1) {
			str[nw + nrb] = s[i];
			nrb++;
		}
	}

	int len = nw + nrb;
	for (int i = 0; i < len; i++) {
		if ((str[i] == 'B' && str[i + kb] == 'B') || (str[i] == 'R' && str[i + kr] == 'R')) {
			return -1;
		}
	}
	return len;
}

int main() {

	cin >> kr >> kb >> s;
	int limit = 1 << 20;
	int ans = -1;
	for (int i = 0; i < limit; i++) {
		ans = max(ans, check(i));
	}
	cout << ans << endl;
	return 0;
}