include[HTML_REMOVED]
using namespace std;
string a,b;
void fun(int i)
{
if(a[i]==’o’)
a[i]=’*’;
else
a[i]=’o’;
}
int main()
{
int len1,len2,ans=0;
cin>>a>>b;
len1=a.size();
len2=b.size();
for(int i=0;i<len1;i){
if(a[i]!=b[i]){
fun(i);
fun(i+1);
ans;
}
}
cout<<ans<<endl;
return 0;
}