#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); 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;

bool cmp(pair<LL, LL> a, pair<LL, LL> b)
{
	return a.F * b.S <= a.S * b.F;
}

int main()
{
	ios::sync_with_stdio(0); 
	cin.tie(0);
	cout << fixed << setprecision(15);
	
	int n, c;
	LL p, q;
	cin >> n >> c >> p >> q;
	string s;
	cin >> s;
	VI x(n + 1), y(n + 1);
	FOR (i, 1, n + 1)
	{
		if (s[i - 1] == 'Y')
			x[i]++;
		else
			y[i]++;
		y[i] += y[i - 1] + x[i];
		x[i] += x[i - 1];
	}
	VI dp(n + 1, 0);
	VI b = {0};
	FOR (i, 1, n + 1)
	{
		FOR (j, 0, min(SZ(b), c + 1))
		{
			int k = b[SZ(b) - 1 - j];
			dp[i] = max(dp[k], dp[i]);
			PII pr = {x[i] - x[k], y[i] - y[k]};
			//cerr << "X " << i << ' ' << j << ' ' << pr.F << ' ' << pr.S << '\n';
			if (k + c <= i && cmp(MP(p, q), pr))
			{
				dp[i] = max(dp[i], dp[k] + 1);
			}
		}
		int k = b.back();
		PII pr = {x[i] - x[k], y[i] - y[k]};
		if (dp[i] > dp[k] || (dp[i] == dp[k] && cmp(pr, MP(p, q))))
			b.PB(i);
		//cerr << i << ' ' << dp[i] << ": ";
		//for (auto to : b)
		//	cerr << to << ' ';
		//cerr << '\n';
	}
	
	cout << dp[n] << '\n';
	
	return 0;
}