D = int(input())
C1 = input()
C2 = input()
days = 'x'*D+C1+C2+'x'*D
ans = 0

for i in range(len(days)-D+1):
    days_ = ''
    
    for j in range(len(days)):
        if i<=j<i+D:
            days_ += 'o'
        else:
            days_ += days[j]
    
    r = 0
    c = 0
    
    for l in range(len(days_)):
        while r<len(days_) and days_[r]=='o':
            c += 1
            r += 1
        
        ans = max(ans, r-l)
        
        if l==r:
            r += 1
        else:
            if days_[l]=='o':
                c -= 1

print(ans)