#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 LineBase{
	int p[13];
	void clear(){
		memset(p,0,sizeof p);
	}
	void insert(ll x){
		for(int i=12;~i;--i){
			if(!(x>>i)) continue;
			if(!p[i]){
				p[i]=x; break;
			} x^=p[i];
		}
	}
	int query(){
		int ans=0;
		for(int i=12;~i;i--) ans=max(ans,ans^p[i]);
		return ans;
	}
}f[1035][1035];
void merge(LineBase &t1,LineBase &t2){
	for(int i=0;i<=12;i++) t1.insert(t2.p[i]);
}
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++){
			merge(f[i][j],f[i-1][j-v]);
			f[i][j].insert(w);
		}
	} 
	if(dp[m]) cout<<f[n][m].query()<<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();
}