#include<bits/stdc++.h>
#define poly vector<int>
#define IOS ios::sync_with_stdio(false)
#define ll long long
#define mp make_pair
#define mt make_tuple
#define pa pair < int,int >
#define fi first
#define se second
#define inf 1e18
#define mod 998244353
#define sz(x) ((int)((x).size()))
#define int ll
// #define N 
using namespace std;
const int N=500005;
int n,c,p,q,a[N],s[N],b[N];
void BellaKira()
{
    cin>>n>>c>>p>>q;
    for (int i=1;i<=n;i++)
    {
        char c;
        cin>>c;
        if (c=='Y') a[i]=1;
        else a[i]=0;
    }
    for (int i=1;i<=n;i++)
    {
        s[i]=s[i-1]+a[i];
        b[i]=b[i-1];
        bool bl=0;
        for (int j=i-c+1;j>=i-3*c&&j>=1;j--)
            if (b[j-1]==b[i])
            {
                if ((s[i]-s[j-1])*q>=p*(i-j+1)) bl=1;
            }
        if (bl) b[i]++;
    }
    cout<<b[n]<<'\n';

}
signed main()
{
    IOS;
    cin.tie(0);
    int T=1;
    while (T--)
    {
        BellaKira();
    }
}
/*list:
1.mod 998244353 or 1e9+7 or ???
2.N
3.duipai shuju xingtai duoyidian
...
*/