import java.util.*;
public class Main
{
static int n,ans;
static char[] a,b;
static void dfs(int u)
{
if(u==n-1)return ;
if(a[u]!=b[u])
{
ans++;
if(a[u]=='*')a[u]='o';else a[u]='*';
u++;
if(a[u]=='*')a[u]='o';else a[u]='*';
u--;
}
dfs(u+1);
}
public static void main(String [] args)
{
Scanner sc=new Scanner(System.in);
a=sc.next().toCharArray();
b=sc.next().toCharArray();
n=a.length;
dfs(0);
System.out.println(ans);
}
}