#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned ll
#define endl "\n"
#define PII pair<int,int>
const ll INF=0x3f3f3f3f;//3f3f3f3f;
const int mod=1e9+7;
const int N=2e6+5;
struct LBase{
    int d[13];
    void clear() { memset(d,0,sizeof d);}
    bool insert(int x) {
        for(int i =12;i>=0;--i)
            if (x & (1 << i)) {
                if (d[i]) x ^= d[i];
                else {d[i] = x; break;}
            }
        return x > 0;
    }
    int qmax() {
        int x = 0;
        for (int i = 12; i >= 0; --i)
            if (d[i])
                if ((x ^ d[i]) > x) x ^= d[i];
        return x;
    }
    void merge(const LBase &a) {
        for (int i = 12; i >= 0; --i)
            if(a.d[i]) insert(a.d[i]);
    }
}f[1028][1028];
bitset<1035>dp;
void solve(){
	int n,m; cin>>n>>m;
	for(int i=1;i<=n;i++){
		for(int j=0;j<=m;j++) f[i][j].clear();
	}
	dp.reset(); dp[0]=1;
	for(int i=1;i<=n;i++){
		int v,w; cin>>v>>w;
		for(int j=0;j<=m;j++) f[i][j]=f[i-1][j];
		for(int j=m;j>=v;j--) if(dp[j-v]) dp[j]=1;
		for(int j=v;j<=m;j++){
			f[i][j].merge(f[i-1][j-v]);
			f[i][j].insert(w);
		}
	} 
	if(dp[m]) cout<<f[n][m].qmax()<<endl;
	else cout<<-1<<endl;
}
int main(){
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	int T=1; cin>>T;
    while(T--) solve();
}