import re

def get_max_holidays(weekly):
    holiday = 0
    for m in re.findall('o+', weekly):
        holiday = max(holiday, len(m))
    return holiday

def solve(d, GW):
    ans = 0   
    for i in range(42 - d+1):
        gw = GW[:]
        for j in range(i, i+d):
            if gw[j] == 'x':
                gw[j] = 'o'
            else:
                break
        gw_str = ''.join(gw)
        ans = max(ans, get_max_holidays(gw_str))
    return ans

def main():
    d = int(input())
    w1 = input()
    w2 = input()
    workday = 'xxxxxxx'
    GW = list(workday * 2 + w1 + w2 + workday * 2)
    print(solve(d, GW))

if __name__ == '__main__':
    main()