#include <algorithm>
#include <iostream>
#include <cstdio>
#include <map>
#include <numeric>
#include <cmath>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <complex>
#include <string.h>
#include <unordered_set>
#include <unordered_map>
#include <tuple>
#include <iomanip>
using namespace std;

#define endl '\n'
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define uniq(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

typedef long long ll;
typedef pair<int, int> P;
typedef unsigned int uint;
typedef unsigned long long ull;
struct pairhash {
public:
    template<typename T, typename U>
    size_t operator()(const pair<T, U> &x) const {
	size_t seed = hash<T>()(x.first);
	return hash<U>()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
};

const int inf = 1000000009;
const double eps = 1e-8;

bool calc(int kr, int kb, string s, int bit) {
    vector<char> vs;
    int count = 0;
    for (int i = 0; i < 30; i++) {
	if (s[i] == 'R' || s[i] == 'B') {
	    if (!((bit>>count)&1))
		vs.push_back(s[i]);
	    count++;
	} else {
	    vs.push_back('W');
	}
    }
    int len = vs.size();
    for (int i = 0; i < len; i++) {
	if (vs[i] == 'R') {
	    if ((i - kr >= 0 && vs[i-kr] == 'R') || (i + kr < len && vs[i+kr] == 'R')) return false;
	} else if (vs[i] == 'B') {
	    if ((i - kb >= 0 && vs[i-kb] == 'B') || (i + kb < len && vs[i+kb] == 'B')) return false;	    
	}
    }
    return true;
}

inline int bitcount(int x) {
    int ret = 0;
    while (x) {
	x &= x - 1;
	ret++;
    }
    return ret;
}


int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);

    int kr, kb;
    cin >> kr >> kb;
    string s;
    cin >> s;
    int res = 0;
    for (int i = 0; i < (1<<20); i++) {
	if (calc(kr, kb, s, i))
	    res = max(res, 30 - bitcount(i));
    }
    cout << res << endl;
}