#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
const int N = 105;
char s1[N], s2[N];
int main()
{
cin >> s1 >> s2;
int res = 0;
for (int i = 0; i < strlen(s1) - 1; i ++ )
{
if (s1[i] != s2[i])
{
res ++ ;
if (s1[i + 1] == '*') s1[i + 1] = 'o'; //其实只用翻转后一元素即可,当前元素翻不翻都无所谓
else s1[i + 1] = '*';
}
}
cout << res << endl;
return 0;
}