#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>

using namespace std;

const int N = 110;

char start[N],aim[N];
int res = 0;

void turn(int u){
    if(start[u] == '*') start[u] = 'o';
    else    start[u] = '*';
}

int main(){
    cin >> start >> aim;
    int n = strlen(start);
    for(int i = 0;i < n - 1;++i){
        if(start[i] != aim[i]){
            turn(i),turn(i + 1);
            res++;
        }
    }
    cout << res << endl;
    return 0;
}