#include <bits/stdc++.h>
using namespace std;
const double eps = 0.000001;
const long double pi = acos(-1);
const int maxn = 1e7 + 9;
const int mod = 1e9 + 7;
const long long MOD = 1e18 + 9;
const long long INF = 1e18 + 123;
const int inf = 2e9 + 11;
const int mxn = 1e6 + 9;
const int N = 5e3 + 123;
const int NN = 5e5 + 123;
const int PRI = 555557;
const int pri = 997;
int tests = 1;
int n, m, k, pre[NN], ans, l, r, a, b, t;
char s[NN];
bool check(int x) {
  for (int i = 1; i <= x; i++) {
    long long dis = min(2 * (i - 1) + (x - i), 2 * (x - i) + (i - 1));
    if (pre[i] + pre[n] - pre[n - (x - i)] + dis * a <= t) return 1;
  }
  return 0;
}
inline void Solve() {
  cin >> n >> a >> b >> t;
  for (int i = 1; i <= n; i++) cin >> s[i];
  for (int i = 1; i <= n; i++) {
    pre[i] = pre[i - 1] + (s[i] == 'w') * b + 1;
  }
  l = 1, r = n;
  while (l <= r) {
    int mid = (l + r) / 2;
    if (check(mid)) {
      ans = mid;
      l = mid + 1;
    } else
      r = mid - 1;
  }
  cout << ans;
}
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0);
  while (tests--) {
    Solve();
  }
}
