#include <iostream>
#include <string>
#include <cstdlib>

using namespace std;

int kr, kb;

int length(string& s, int begin, bool remove) {
	int i;
	for (i = begin; i < s.size() && s[i] == 'W'; ++i) {
	}
	if (i == s.size()) {
		string shrunk;
		for (size_t k = 0; k < s.size(); ++k) {
			if (s[k] != '-') {
				shrunk.push_back(s[k]);
			}
		}
		bool invalid = false;
		for (int k = 0; k < shrunk.size() && !invalid; ++k) {
			if (shrunk[k] == 'R') {
				if (k >= kr) {
					invalid |= (shrunk[k - kr] == 'R');
				}
				if (k + kr < shrunk.size()) {
					invalid |= (shrunk[k + kr] == 'R');
				}
			} else if (shrunk[k] == 'B') {
				if (k >= kb) {
					invalid |= (shrunk[k - kb] == 'B');
				}
				if (k + kb < shrunk.size()) {
					invalid |= (shrunk[k + kb] == 'B');
				}
			}
		}
		return invalid ? -1 : shrunk.size();
	}
	char old = s[i];
	if (remove) {
		s[i] = '-';
	}
	int result = max(length(s, i + 1, true), length(s, i + 1, false));
	s[i] = old;
	return result;
}

int main() {
	string s;
	cin >> kr >> kb >> s;
	int result = max(length(s, 0, true), length(s, 0, false));
	cout << result << endl;
	return 0;
}