def turnCoin(n,m):
    indexm = 0
    result = 0
    listn= []
    listm = []

    for i in n:
        listn.append(i)
    for i in m :
        listm.append(i)

    for indexn in range(len(n)):
        if listn[indexn] != listm[indexm]:
            if listn[indexn+1] == "*":
                listn[indexn+1] = "o"
            else:
                listn[indexn+1] = "*"
            result += 1
        indexm += 1
    return result

n=input()
m=input()
print(turnCoin(n,m))