#include <bits/stdc++.h>
#define syosu(x) fixed<<setprecision(x)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<string> vs;
typedef vector<P> vp;
typedef vector<vp> vvp;
typedef vector<pll> vpll;
typedef pair<int,P> pip;
typedef vector<pip> vip;
const int inf=1<<30;
const ll INF=1ll<<60;
const double pi=acos(-1);
const double eps=1e-8;
const ll mod=1e9+7;
const int dx[4]={-1,0,1,0},dy[4]={0,-1,0,1};

const int M=30;
int A,B,a[M];
vi b;

int main(){
	cin>>A>>B;
	for(int i=0;i<M;i++){
		char c;
		cin>>c;
		if(c=='R') a[i]=1;
		if(c=='B') a[i]=2;
		if(c!='W') b.push_back(i);
	}
	int res=10;
	for(int i=0;i<1<<20;i++){
		vi c(M),d;
		for(int j=0;j<20;j++) if(i&1<<j) c[b[j]]++;
		for(int j=0;j<M;j++) if(!c[j]) d.push_back(a[j]);
		int n=d.size();
		bool flag=1;
		for(int j=0;j<n;j++){
			if(d[j]==1&&(j>=A&&d[j-A]==1||j+A<n&&d[j+A]==1)) flag=0;
			if(d[j]==2&&(j>=B&&d[j-B]==2||j+B<n&&d[j+B]==2)) flag=0;
		}
		if(flag) res=max(res,n);
	}
	cout<<res<<endl;
}