python3 枚举
a = list(input())
b = list(input())
res = 0
for i in range(len(a)):
if (a[i] != b[i]):
res += 1
if (i < len(a)-1 and a[i+1] == '*'):
a[i+1] = 'o'
continue
if (i < len(a)-1 and a[i+1] == 'o'):
a[i+1] = '*'
print(res)