D=int(input())
C=('x'*7)+input()+input()+('x'*7)
ans = 0
for i in range(28-D):
	if i == 0 or C[i-1]=='o':
		j=0
		while i+j<28 and C[i+j]=='x':
			j+=1
		if j==D:
			c=C[:i]+('o'*D)+C[i+D:]
			for k in range(1,29):
				if ('o'*k) in c:
					ans = max(ans,k)
print(ans)