#include <bits/stdc++.h>
using namespace std;
const int N = 2e6;
int cost[N], n, a, b, T;
string s;
long long l[N], r[N];
bool check(int d) {
  --d;
  long long bst = min(l[d], r[d]);
  for (int i = 1; i < d; ++i) {
    bst = min(bst, l[i] + r[d - i] + a * i);
    bst = min(bst, r[i] + l[d - i] + a * i);
  }
  return bst + d + 1 + cost[0] <= T;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n >> a >> b >> T;
  cin >> s;
  for (int i = 0; i < s.size(); ++i) {
    cost[i] = (s[i] == 'w' ? b : 0);
  }
  for (int i = 1; i < n; ++i) {
    r[i] = r[i - 1] + cost[i] + a;
  }
  for (int i = 1; i < n; ++i) {
    l[i] = l[i - 1] + cost[n - i] + a;
  }
  int L = 0, R = n + 1;
  while (R - L > 1) {
    int m = (L + R) >> 1;
    if (check(m))
      L = m;
    else
      R = m;
  }
  cout << L;
  return 0;
}
