#pragma GCC optimize(2)
#include <bits/stdc++.h>
#define int long long
#define pi 3.1415926
typedef long long ll;
using namespace std;
int mod=998244353;

int fp(int a,int b){
	int ans=1;
	while(b){
		if(b&1) ans*=a,ans%=mod;
		a*=a,a%=mod;
		b>>=1;
	}
	return ans;
}

void solve(){
	int n,c,q,p;cin>>n>>c>>p>>q;
	int ans=0;
	string str;cin>>str;
	int p1=0,p2=1;
	vector<int> pre(n+1);
	for(int i=1;i<=n;i++){
		if(str[i-1]=='Y') pre[i]++;
		pre[i]+=pre[i-1];
		p1++;
		//cout<<p2<<" "<<p1<<endl;
		if(p1-p2+1>=c){
			if((pre[p1]-pre[p2-1])*q>=(p1-p2+1)*p) p2=p1+1,ans++;
			else{
				if(p1-p2+1>c&&(pre[p1-c]-pre[p2-1])*q<(p1-c-p2+1)*p) p2=p1-c+1;
				if((pre[p1]-pre[p2-1])*q>=(p1-p2+1)*p) p2=p1+1,ans++;
			}
		}
	}
	cout<<ans;
}

signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	//int t;cin>>t;while(t--) 
	solve();
	return 0;
}