#include<bits/stdc++.h>
#define irep(i,l,r) for(int i = l; i <= r; ++i)
#define drep(i,r,l) for(int i = r; i >= l; --i)
#define ceil(pp,qq) (((pp)>0)^((qq)>0)?-Abs(pp)/Abs(qq):(pp)%(qq)?(pp)/(qq)+1:(pp)/(qq))
#define floor(pp,qq) (((pp)>0)^((qq)>0)?-ceil(Abs(pp),Abs(qq)):(pp)/(qq))
#define ll long long
#define LL __int128
using namespace std;
ll Abs(ll x){return x > 0 ? x : - x;}
inline ll read(){
	char ch = getchar();
	ll s = 0; bool w = 0;
	while(!isdigit(ch)){if(ch == '-')w = 1;ch = getchar();}
	while(isdigit(ch))s = (s << 3) + (s << 1) + (ch ^ 48), ch = getchar();
	return w ? - s : s;
}

const int itinf = 1e9;
const ll llinf = 4e18;
const int mod = 1000000007;
const int N = 500009;

inline int mul(int nma, int nmb){
	return ((1ll * nma * nmb % mod) + mod) % mod;
}

void solve(){
	int n = read(), m = read();
	vector<bitset<1024>>f(1024),g(1024);
	/*
	f[xor][weight]
	*/
	f[0][0] = 1;
	for(int it = 0; it < n; ++ it){
		int w = read(), v = read();
		for(int xr = 1023 ; xr >= 0; -- xr){
			g[xr ^ v] = f[xr ^ v] | (f[xr] << w);
		}
		swap(f, g);
		g.resize(1024);
	}
	for(int i = 1023; i >= 0; -- i){
		if(g[i][m]){
			printf("%d\n", i);
			return;
		}
	}
	puts("-1");
	return;
}

int main(){
	int T = read();
	while(T --){
		solve();
	}
	return 0;
}