#include <bits/stdc++.h>
using namespace std;
int main(){
int s[2][110];
int d[5][110]={0};
int l;
string str;
cin>>str;
for (int i=0;i<str.size();++i){
if (str[i]=='0') s[0][i]=0;
else s[0][i]=1;
}
cin>>str;
for (int i=0;i<str.size();++i){
if (str[i]=='0') s[1][i]=0;
else s[1][i]=1;
}
l = str.size();
if (l==1) return cout<<"0"<<endl, 0;
for (int i=0;i<l-1;++i){
for (int j=0;j<5;++j){
//not put
if (j==0){
if (s[0][i+1]==0 && s[1][i+1]==0){
if (s[0][i]==0) d[3][i+1]=max(d[3][i+1],d[j][i]+1);
if (s[1][i]==0) d[4][i+1]=max(d[4][i+1],d[j][i]+1);
}
if (s[0][i]==0 && s[1][i]==0){
if (s[0][i+1]==0) d[1][i+1]=max(d[1][i+1],d[j][i]+1);
if (s[1][i+1]==0) d[2][i+1]=max(d[2][i+1],d[j][i]+1);
}
for (int k=0;k<5;++k){
d[k][i+1]=max(d[k][i+1],d[j][i]);
}
}
else if (j==3 || j==4){
for (int k=0;k<5;++k){
d[k][i+1]=max(d[k][i+1],d[j][i]);
}
}
else if (j==1){
if (s[0][i+1]==0 && s[1][i+1]==0){
if (s[1][i]==0) d[4][i+1]=max(d[4][i+1],d[j][i]+1);
}
for (int k=0;k<5;++k){
d[k][i+1]=max(d[k][i+1],d[j][i]);
}
}
else if (j==2){
if (s[0][i+1]==0 && s[1][i+1]==0){
if (s[0][i]==0) d[3][i+1]=max(d[3][i+1],d[j][i]+1);
}
for (int k=0;k<5;++k){
d[k][i+1]=max(d[k][i+1],d[j][i]);
}
}
}
}
int ans=0;
for (int i=0;i<5;++i){
ans = max(ans, d[i][l-1]);
}
cout<<ans<<endl;
}
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