#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

int main() {
    int N, C; long long P, Q;
    cin >> N >> C >> P >> Q;
    string Z;
    cin >> Z;
    vector<long long> S(N + 1);
    for (int i = 0; i < N; i++) {
        S[i + 1] = S[i] + (Z[i] == 'Y' ? Q - P : -P);
    }
    int pos = 0, rank = 0;
    while (pos <= N - C) {
        long long curmin = S[pos];
        bool f = false;
        for (int i = pos + C; i <= N; i++) {
            curmin = min(curmin, S[i - C]);
            if (curmin <= S[i]) {
                f = true;
                pos = i;
                break;
            }
        }
        if (!f) {
            break;
        }
        rank++;
    }
    cout << rank << endl;
    return 0;
}