
n, a, b, T = map(int, raw_input().split())
pos = raw_input()

visited = [False] * n
nr_visited = 0
first_time = 1 + b * (pos[0] != 'h')
if T >= first_time:
    T -= first_time
    visited[0] = 1
    nr_visited += 1
    last_pos = pos[0]
    left = n-1
    right = 1
    while T > 0 and left >= right and nr_visited < n:
        left_t = a + 1 + b * (pos[left] != 'h')
        right_t = a + 1 + b * (pos[right] != 'h')
        if T < min(left_t, right_t):
            break
        if left_t <= right_t:
            visited[left] = 1
            nr_visited += 1
            left -= 1
            T -= left_t
        else:
            visited[right] = 1
            nr_visited += 1
            right += 1
            T -= right_t
    print nr_visited
else:
    print 0
