n, k = map(int, input().split())

types = input().split()         
A = list(map(int, input().split()))

left = 0
total_endurance = 0
enemy_count = 0
max_enemies = 0

for right in range(n):
    total_endurance += A[right]
    if types[right] == 'E':
        enemy_count += 1

    while total_endurance > k:
        total_endurance -= A[left]
        if types[left] == 'E':
            enemy_count -= 1
        left += 1

    max_enemies = max(max_enemies, enemy_count)

print(max_enemies)