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

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, b, a) for(int i = (b) - 1; i >= (a); i--)
#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;



struct Fewick
{
	int n;
	VI t;
	void init(int _n)
	{
		n = _n;
		t.clear();
		t.resize(n, 0);
	}
	void upd(int pos, int val)
	{
		for(;pos < n; pos |= pos + 1)
			t[pos] = max(t[pos], val);
	}
	int query(int pos)
	{
		int res = 0;
		for(;pos >= 0; pos = (pos & (pos + 1)) - 1)
			res = max(res, t[pos]);
		return res;
	}
};


int main()
{
	ios::sync_with_stdio(0); 
	cin.tie(0);
	cout << fixed << setprecision(15);
	
	LL n, c, p, q;
	cin >> n >> c >> p >> q;
	string s;
	cin >> s;
	VI pref(n + 1, 0);
	FOR(i, 0, n)
		pref[i + 1] = pref[i] + (s[i] == 'Y');
	
	vector<LL> vals(n + 1);
	FOR(i, 0, n + 1)
		vals[i] = q * pref[i] - p * i;
	sort(ALL(vals));
	
	
	Fewick T;
	T.init(n + 1);
	
	VI dp(n + 1, 0);
	FOR(i, 0, n + 1)
	{
		LL curI = q * pref[i] - p * i;
		int idI = lower_bound(ALL(vals), curI) - vals.begin();
		//j <= i - c && cur_i >= cur_j -> dp[i] = max(dp[j])
		if(i - c >= 0)
		{
			LL curJ = q * pref[i - c] - p * (i - c);
			int idJ = lower_bound(ALL(vals), curJ) - vals.begin();
			T.upd(idJ, dp[i - c] + 1);
		}
		if(i)
			dp[i] = max(dp[i - 1], T.query(idI));
		
		//cout << dp[i] << " ";
	}
	cout << dp[n] << "\n";
	
	
	
	
	
		
	
	
	
	
	
	
	return 0;
}