include[HTML_REMOVED]
using namespace std;
int main(){
string a,b;
int jishu=0;
cin>>a>>b;
for(int i=0;i<a.length();i){
if(b[i]==a[i]);
else{
for(int j=i;j<=i+1;j){
if(a[j]==’o’) a[j]=’*’;
else a[j]=’o’;
}
jishu++;
}
}
cout<<jishu;
return 0;
}