#include<iostream>
#include<cstring>
using namespace std;
const int N=1010;
char s1[N],s2[N];
void turn(int x){
if(s1[x]=='*'){
s1[x]='o';
}else{
s1[x]='*';
}
}
int main(){
cin>>s1>>s2;
int n=strlen(s1);
int res=0;
for(int i=0;i<n;i++){
if(s1[i]!=s2[i]){
turn(i),turn(i+1);
res++;
}
}
cout<<res<<endl;
return 0;
}