a=list(input())

b=list(input())

length = len(a)

s = 0

for i in range(length):

if a[i]!= b[i]:

    s+=1
    
    if b[i] == "*":
    
        b[i] = "o"
    else
    :
    
        b[i]="*"
        
        if i < length - 1:
        
            if b[i + 1] == "*":
            
                b[i + 1] = "o"
            else:
            
                b[i + 1] = "*"

print(s) 求大神指点那儿错啦