#include <bits/stdc++.h>
using namespace std;

int main(void) {
	int Kr, Kb;
	cin >> Kr >> Kb;
	string S;
	cin >> S;
	
	vector<int> v;
	for(int i = 0; i < 30; ++i) if(S[i] != 'W') v.push_back(i);
	
	int ans = -1;
	for(int bit = 0; bit < (1 << 20); ++bit) {
		vector<bool> ok(30, true);
		for(int i = 0; i < 20; ++i) if(bit >> i & 1) ok[v[i]] = false;
		
		string T = "";
		for(int i = 0; i < 30; ++i) if(ok[i]) T += S[i];
		int M = T.size();
		
		bool flag = true;
		for(int i = 0; i < M; ++i) {
			if(T[i] == 'R' and i + Kr < M and T[i + Kr] == 'R') flag = false;
			if(T[i] == 'B' and i + Kb < M and T[i + Kb] == 'B') flag = false;
		}
		
		if(flag) ans = max(ans, M);
	}
	
	cout << ans << endl;
	
	return 0;
}