# -*- coding: utf-8 -*-

'''
問題の解釈がうまくできないのでやめる（好きではない問題だった）
'''

D = int(input())
C = input()
C += input()

maru = batsu = 0
weekday = True
cont_list = []
for c in C:
    if weekday and c=='o':
        maru += 1
    elif weekday and c=='x':
        cont_list.append(maru)
        batsu = 1
        weekday = False
    elif not weekday and c=='x':
        batsu += 1
    elif not weekday and c=='o':
        cont_list.append(batsu)
        maru = 1
        weekday = True
if weekday:
    cont_list.append(maru)
else:
    cont_list.append(batsu)

ans = 0
for i in range(1, len(cont_list), 2):
    if D >= cont_list[i]:
        diff = D - cont_list[i]
        if cont_list[i-1]==0 and i+1<len(cont_list):
            ans = max(ans, diff+cont_list[i]+cont_list[i+1])
        elif i+1<len(cont_list):
            ans = max(ans, cont_list[i-1]+cont_list[i]+cont_list[i+1])
        else:
            ans = max(ans, cont_list[i-1]+cont_list[i]+diff)
    else:
        if i+1<len(cont_list):
            ans = max(ans, cont_list[i-1]+D, D+cont_list[i+1])
        else:
            ans = max(ans, cont_list[i-1]+D)

print(ans)