N = int(input())
S = list(map(int,input().split()))
T = list(map(int,input().split()))
X = [-1] * N
Y = [-1] * N
X1 = []
Y1 = []
for i in range(N):
    if S[i] == 0:
        X[i] = 0
    elif S[i] == 2:
        X[i] = N
        for j in range(N):
            if Y[j] == -1:
                Y[j] = 1
            elif Y[j] < N:
                Y[j] += 1
    else:
        X1.append(i)
    if T[i] == 0:
        Y[i] = 0
    elif T[i] == 2:
        Y[i] = N
        for j in range(N):
            if X[j] == -1:
                X[j] = 1
            elif X[j] < N:
                X[j] += 1
    else:
        Y1.append(i)
i = 0
for x in X1:
    if X[x] == -1:
        X[x] = 1
        if -1 in Y:
            Y[Y.index(-1)] = 1
        else:
            while i < N and (Y[i] == 0 or Y[i] == N):
                i += 1
            if i < N:
                Y[i] += 1
i = 0
for y in Y1:
    if Y[y] == -1:
        Y[y] = 1
        if -1 in X:
            X[X.index(-1)] = 1
        else:
            while i < N and (X[i] == 0 or X[i] == N):
                i += 1
            if i < N:
                X[i] += 1
print(sum(X))