#include<bits/stdc++.h>
using namespace std;
int main(){
	string a,b;
	int j=0;
	cin>>a>>b;
	for(int i=0;i<a.size();i++){
		if(a[i]!=b[i]){
			if(a[i]=='*'){
				a[i]='o';
				if(a[i+1]=='*') a[i+1]='o';
				else a[i+1]='*';
			}
			else{
				a[i]='*';
				if(a[i+1]=='*') a[i+1]='o';
				else a[i+1]='*';
			}
			j++;
		}
	} 
	cout<<j;
	return 0;
}

额...原本以为这点代码肯定会WA的...没想到竟然A了