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

for d in range(D+1):
    for i in range(len(days)-d+1):
        if days[i:i+d]!='x'*d:
            continue
    
        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)