#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 110;
int n;
char start[N],aim[N];
void turn(int i)
{
    if(start[i]=='*')start[i]='o';
    else start[i] = '*';
}
int main()
{
    cin>>start>>aim;
    n = strlen(start);
    int res = 0;
    for(int i=0;i<n-1;i++)
    {
        if(start[i] != aim[i])
        {
            turn(i),turn(i+1);
            res++;
        }
    }
    cout << res<<endl;

    return 0;
}