#include <bits/stdc++.h>
using namespace std;
const int MAX = 5e5 + 5;
int n, a, b, t, z, c[MAX * 2], ans;
char k;
int main() {
  cin >> n >> a >> b >> t;
  for (int i = 0; i < n; i++)
    cin >> k, z += c[i] = c[n + i] = (k == 'w') * b + 1;
  z -= c[0];
  int l = 1, r = n;
  while (l <= n and r < 2 * n) {
    z += c[r++];
    while (r - l > n or z + (r - l - 1 + min(n - l, r - n - 1)) * a > t)
      z -= c[l++];
    if (l > n) break;
    ans = max(ans, r - l);
  }
  printf("%d", ans);
}
