#include<bits/stdc++.h>
#define endl "\n"
#define int long long
using namespace std;
#define pii pair<int, int>
#define rep(i, a, b) for(int i = a; i <= b; i ++ )
#define pre(i, a, b) for(int i = a; i >= b; i -- )
#define IOS ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
const int N = 1e6 + 10;
int n, m, k;
bitset<2024>dp[2][2024];
void solve()
{
    cin >> n >> m;
    rep(i, 0, 2000) dp[0][i].reset(), dp[1][i].reset();
    dp[0][0] = 1;
    dp[1][0] = 1;
    rep(i, 1, n)
    {
        int v, w;
        cin >> v >> w;
        if(i==1)continue;
        rep(j, 0, 1030)
        {
            dp[1][j] |= (dp[0][j ^ w] << v);
        }
        // if(i==1)cout<<dp[1][4];
        rep(j, 0, 1030) dp[0][j] = dp[1][j];
    }
    int ans = -1;
    rep(i, 0, 1030)
    {
        if(dp[0][i][m]) ans = i;
    }
    cout << ans << endl;
}
signed main()
{
    IOS;
    int _;
    _ = 1;
    cin >> _;
    while(_ -- )
    {
        solve();
    }
	
	return 0;
}