#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 110;
int n;
char start[N],ans[N];//分别表示初始给的字符串和答案最终要的字符串
void turn (int x)
{
    if(start[x] == '*') start[x] = 'o';
    else start[x] = '*';
}
int main()
{
    cin >> start >> ans;
    n  = strlen(start);
    int res = 0;
    for(int i = 0; i < n-1;i++)
        if(start[i] != ans[i])
        {
            turn(i),turn(i+1);
            res ++;
        }
    cout << res << endl;
    return 0;
}