#include <iostream>
using namespace std;
string tmp, s;  
void turn(int index){
    s[index] = (s[index] == '*' ? 'o' : '*');
    s[index + 1] = (s[index + 1] == '*' ? 'o' : '*'); 
}
int main(){
    cin >> tmp >> s;
    int cnt = 0;
    for(int i = 0; i < s.size() - 1; i ++ ){
        if(s[i] != tmp[i]){
            turn(i);
            cnt ++ ;
        }
    }
    cout << cnt << endl;
}