import java.io.*;
class Main{
static BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
public static void main(String[] args) throws Exception{
char[] a = read.readLine().toCharArray(), b = read.readLine().toCharArray();
int n = a.length;
int ans = 0;
for(int i = 0; i < n; i++){
if(a[i] != b[i]){
ans++;
a[i] = b[i];
a[i+1] = a[i+1] == '*' ? 'o': '*';
}
}
System.out.println(ans);
}
}