#include <bits/stdc++.h>

using namespace std;

const int maxn = 5e5 + 5;

int n, c, p, q;
char s[maxn];
int sum[maxn], pos[maxn], f[maxn];
long long a[maxn];
vector<long long> vec;

int main(){
	scanf("%d%d%d%d", &n, &c, &p, &q);
	scanf("%s", s + 1);
	for (int i = 1; i <= n; ++i) {
		if (i) sum[i] = sum[i - 1] + (s[i] == 'Y');
		a[i] = 1ll * q * sum[i] - 1ll * p * i;
		// printf("i = %d sum = %lld a = %lld\n", i, sum[i], a[i]);
	}
	long long mn = 1e18;
	
	int ans = 0, lst = 0;
	for (int i = 0; i <= n; ++i) {
		// printf("upd %d %d\n", i - c, lst);
		if (i - c >= 0 && i - c >= lst) mn = min(mn, a[i - c]);
		// printf("i = %d a = %lld mn = %lld ans = %d\n", i, a[i], mn, ans);
		if (mn <= a[i]) ++ans, lst = i, mn = 1e18;
	}
	
	printf("%d\n", ans);
	return 0;
}