d = int(input())
week = list(input())+list(input())
maxholi = 0

def search(wek,i,cnt):
    global maxholi
    while cnt>0 and i<14:
        if wek[i]=="o":
            break
        wek[i]="o"
        cnt -= 1
        i += 1
    cnt = 0
    for i in range(14):
        if wek[i]=="o":
            cnt += 1
            maxholi = max(maxholi,cnt)
        else:
            cnt = 0

for i in range(14):
    if week[i]=="x":
        search(week[:],i,d)
search(week,0,0)
print(maxholi)