#include<bits/stdc++.h>
using namespace std;
int main()
{
    freopen("conversion.in","r",stdin);
    freopen("conversion.out","w",stdout);
    string a,b;
    long long br1=0,br2=0,br=0;
    cin>>a;
    cin>>b;
    for(int i=0;i<a.size();i++){
        if(a[i]=='1')br1++;
        if(a[i]!=b[i])br++;
    }
    for(int i=0;i<b.size();i++){
        if(b[i]=='1')br2++;
    }
    cout<<abs(br1-br2)+(br-abs(br1-br2))/2<<endl;
return 0;
}