https://codeforces.com/gym/580226/problem/F

#include<bits/stdc++.h>
#define lc p<<1
#define rc p<<1|1
#define INF 2e9
using namespace std;

#define endl '\n'
using ll = long long;
using pii = pair<ll, ll>;
const double PI = acos(-1);
const int N=2e5+10;
void solve(){
	string s1,s2;cin>>s1>>s2;
	int cnt=0;
	for(int i=0;i<s1.size()-1;i++){
		if(s1[i]=='0'&&s1[i+1]=='0'&&s2[i]=='0'){
			s1[i]=s1[i+1]=s2[i]='X';
			cnt++;
		}
		else if(s1[i]=='0'&&s1[i+1]=='0'&&s2[i+1]=='0'){
			s1[i]=s1[i+1]=s2[i+1]='X';
			cnt++;
		}
		else if(s1[i]=='0'&&s2[i]=='0'&&s2[i+1]=='0'){
			s1[i]=s2[i]=s2[i+1]='X';
			cnt++;
		}
		else if(s1[i+1]=='0'&&s2[i]=='0'&&s2[i+1]=='0'){
			s1[i+1]=s2[i]=s2[i+1]='X';
			cnt++;
		}
		else {
			
		}
	}
	cout<<cnt;
}


int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr), cout.tie(nullptr);
	
	int T = 1;
//	cin>>T;
	while (T--) {
		solve();
	}
	
	return 0;
}