import java.util.*;
public class Main{
public static void main(String[]args){
Scanner sc=new Scanner(System.in);
String s1=sc.next();
String s2=sc.next();
char c1[]=s1.toCharArray();
char c2[]=s2.toCharArray();
int res=0;
for(int i=0;i<c1.length-1;i++){
if(c1[i]!=c2[i]){
if(c1[i+1]=='*') c1[i+1]='o';
else c1[i+1]='*';
res++;
}
}
System.out.println(res);
}
}
太秒了