N, K = map(int, input().split())
S = [0] + [1 if a == "x" else 0 for a in input()]
X = [0] * N
l = 10 ** 10
for i in range(N)[::-1]:
    if l - i > K and S[i] == 0:
        X[i] = 1
        l = i
print(l)