#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi  = vector<int>; using vb  = vector<bool>; using vd  = vector<double>; using vl  = vector<ll>;
using vvi = vector<vi>;  using vvb = vector<vb>;   using vvd = vector<vd>;     using vvl = vector<vl>;

#define REP(i,n) for(ll i=0; i<(n); ++i)

ll kr, kb;
string s;
vl pos;

ll recur(ll depth, vb & enable){
	if (depth == pos.size()) {
		string ns; REP(i, s.size()) if (enable[i]) ns.push_back(s[i]);
		REP(i, ns.size()) {
			if (ns[i] == 'W') continue;
			ll d = ns[i] == 'R' ? kr : kb;
			if (i - d >= 0 && ns[i - d] == ns[i]) return -1;
			if (i + d < ns.size() && ns[i + d] == ns[i]) return -1;
		}
		return ns.size();
	}

	ll ans = recur(depth + 1, enable);
	enable[pos[depth]] = false;
	ans = max(ans, recur(depth + 1, enable));
	enable[pos[depth]] = true;
	return ans;
}

int main() {
	cin >> kr >> kb >> s;
	REP(i, s.size()) if(s[i]!='W') pos.push_back(i);

	vb enable(s.size(), true);
	cout << recur(0, enable) << endl;

	return 0;
}