#pragma GCC optimize("Ofast") 
#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define sz(a) (int)(a.size())
#define all(a) a.begin(),a.end()
#define lb lower_bound
#define ub upper_bound
#define owo ios_base::sync_with_stdio(0);cin.tie(0);
#define INF (ll)(1e18)
#define debug(...) fprintf(stderr, __VA_ARGS__),fflush(stderr)
#define time__(d) for(long blockTime = 0; (blockTime == 0 ? (blockTime=clock()) != 0 : false);\
debug("%s time : %.4fs\n", d, (double)(clock() - blockTime) / CLOCKS_PER_SEC))
typedef long long int ll;
typedef long double ld;
typedef pair<ll,ll> PII;
typedef pair<int,int> pii;
typedef vector<vector<int>> vii;
typedef vector<vector<ll>> VII;
ll gcd(ll a,ll b){if(!b)return a;else return gcd(b,a%b);}
int main()
{
	ll n,c,p,q;
	cin>>n>>c>>p>>q;
	vector<int>rank(n+1,0);
	vector<ll>pref(n+1,0);
	ll mn = 1e12;
	for(int i=1;i<=n;i++){
		rank[i] = rank[i-1];
		pref[i] = pref[i-1];
		char ch;
		cin>>ch;
		if(ch=='Y')pref[i]++;
		if(i >= c && rank[i-c] == rank[i]){
			mn = min(mn,q*pref[i-c] - p*(i-c));
		}
		//cout<<i<<" "<<(p+q)*pref[i] - p*i<<'\n';
		if(q*pref[i] - p*i >= mn){
			rank[i]++;
			mn = 1e12;
		}
		//cout<<rank[i]<<" ";
		//cout<<'\n';
	}
	cout<<rank[n]<<'\n';

}