#include <iostream>
using namespace std;
#define lli long long int
lli convertbtod(int n){
    lli j = 0,ans=0;
    while(n>0){
        lli last = n%10;
        ans += (last<<j);
        j++;
        n /= 10;
    }
    return ans; 
}
lli convertdtob(int n){
    int ans=0,p = 1;
    while (n>0){
        ans += p*(n&1);
        p*=10;
        n = n>>1;
    }
    return ans;
}
int main() {
    lli t;
    cin >> t;
    while (t--){
        lli n1,n2,ans = 0,j=0;
        cin >> n1 >> n2;
        n1 = convertbtod(n1);
        n2 = convertbtod(n2);
        while (n1>0 || n2>0){
            int l1 = n1&1;
            int l2 = n2&1;
            if (l1^l2){
                ans = ans|(1<<j);
            }
            j++;
            n1 = n1>>1;
            n2 = n2>>1;
        }
        cout << convertdtob(ans) << endl;
    }
    return 0;    
}