import sys
input = sys.stdin.readline

N, K = map(int, input().split())
S = 'o' + input().rstrip() + 'x'
win = [False] * (N + 1)
cnt = 0
for i in range(1, N)[::-1]:
    if S[i] == 'o' and not win[i + 1]:
        cnt += 1
    if i + K + 1 <= N and S[i + K] == 'o' and not win[i + K + 1]:
        cnt -= 1
    if cnt:
        win[i] = True
for i in range(1, K + 1):
    if not win[i + 1]:
        print(i)
        exit()
print(0)