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

const int N = 5e5+5;

int n, c, p, q;
string str;
ll su[N], f[N], ans;

signed main(){
	ios::sync_with_stdio(0); cin.tie(0);
	cin >> n >> c >> p >> q;
	cin >> str; str = '$'+str;
	int an = -p, ay = q-p;
	for (int i = 1; i <= n; ++i){
		su[i] = su[i - 1];
		if (str[i] == 'Y') 
			su[i] += ay;
		else 
			su[i] += an;
	}
	
	int lst = 0, ai;
	ans = 0;
	for (int i = 1; i <= n; i ++){
		while (i <= n && i - lst < c) 
			i ++;
		if (i > n) break;
		if(str[i] == 'Y') ai = ay;
		else ai = an;
		f[i] = su[i-1] - su[i - c] + ai;
		if (i - lst > c) f[i] = max(f[i], f[i - 1] + ai);
		if (f[i] >= 0) lst = i, ans ++;
	}
	cout << ans << endl;
	return 0;	
}