#include <iostream>
using namespace std;
const int N = 110;
string a, b;
void turn(int i) {
if (a[i] == 'o') a[i] = '*';
else a[i] = 'o';
}
int main() {
cin >> a >> b;
int res = 0;
for (int i = 0; i + 1 < a.size(); i ++) {
if (a[i] != b[i]) {
res ++;
turn(i), turn(i + 1);
}
}
cout << res << endl;
return 0;
}