import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

D = int(readline())
C = ''.join(read().decode().split())

C = 'x' * 15 + C + 'x' * 15

answer = 0
for n in range(1,len(C)):
    for i in range(len(C)):
        if i + n > len(C):
            break
        x = C[i:i+n].count('x')
        if x > D:
            continue
        comp = ('o' + C[i:i+n]).count('ox')
        if comp > 1:
            continue
        answer = n

print(answer)