#include <bits/stdc++.h>
#define int long long

using namespace std;

const int O = 5e5 + 5;
const int N = (1 << 20) + 5;
const int mod = 998244353;
const int inf = 1e18;
int pr[] = {167772161, 469762049, 754974721, 1045430273, 1051721729, 1053818881};

int n, c, p, q, sumY[O], sum[O];

main(){
    ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
    cin >> n >> c >> p >> q;

    int res = 0, last = 0, Max = -inf;
    for (int i = 1; i <= n; ++ i){
        char ch; cin >> ch;
        sum[i] = sum[i - 1] + 1;
        sumY[i] = sumY[i - 1] + (ch == 'Y');

        if (i - c >= last){
            int j = i - c;
            Max = max(Max, -q * sumY[j] + p * sum[j]);
        }

        if (Max + q * sumY[i] - p * sum[i] >= 0){
            res += 1;
            last = i;
            Max = -inf;
        }

        //cout << i << " " << last << " " << res << "\n";
    }

    cout << res;
}
/**
**/