// C.cpp
// author : georgeyucjr
#include <bits/stdc++.h>

using ll = long long;
using ull = unsigned long long;
using i128 = __int128;
using u128 = unsigned __int128;
using arr3 = std ::array<int, 3>;
using arr4 = std ::array<int, 4>;
using pii = std ::pair<int, int>;

#define ALL(vc) std ::begin(vc), std ::end(vc)
#define rep(i, f, t, ...) for (std ::decay<decltype(f + t)>::type i = f, _END_##i = t, ##__VA_ARGS__; i <= _END_##i; ++i)
#define per(i, f, t, ...) for (std ::decay<decltype(f + t)>::type i = f, _END_##i = t, ##__VA_ARGS__; i >= _END_##i; --i)
#define eb emplace_back
#define pb push_back
#define mkp make_pair
#define FILEIO(filename) freopen(filename ".in", "r", stdin), freopen(filename ".out", "w", stdout)
template <class T, class U> inline T ceil(T &&x, U &&y) { return (x > 0 ? (x + y - 1) / y : x / y); }
template <class T, class U> inline T floor(T &&x, U &&y) { return (x > 0 ? x / y : (x - y + 1) / y); }
template <class T, class U> inline T divmod(T &&x, U &&y) { auto &&q = floor(x, y); return mkp(q, x - q * y); }
template <class T> constexpr static T inf = std ::numeric_limits<T>::max() >> 1;
template <class T> inline int SZ(T &&x) { return x.size(); }
template <typename T> inline T Abs(const T &x) { return x < 0 ? -x : x; }
template <typename T> inline T sqr(const T &x) { return x * x; }
template <typename T> inline T Max(const T &x) { return x; }
template <typename T> inline T Min(const T &x) { return x; }
template <typename T, typename U, typename... Args> inline T Max(const T &x, const U &y, const Args &...args) { return x < y ? Max(y, args...) : Max(x, args...); }
template <typename T, typename U, typename... Args> inline T Min(const T &x, const U &y, const Args &...args) { return x < y ? Min(x, args...) : Min(y, args...); }
template <typename T, typename... Args> inline void chkmax(T &d, const Args &...x) { d = Max(d, x...); }
template <typename T, typename... Args> inline void chkmin(T &d, const Args &...x) { d = Min(d, x...); }

using namespace std;

#ifdef georgeyucjr
#include <georgeyucjr/debug.h>
#else
#define dbg(...) 36
#endif

namespace easy_IO {
inline void read(char &c) { c = getchar(); }
inline void read(string &str, bool is_move = false) { if (is_move) str += ' '; char c = getchar(); while (c != ' ' && c != '\n') str += c, c = getchar(); }
template <typename T> inline void read(T &x, bool is_unsigned = false) { x = 0; char ch = getchar(); if (is_unsigned) { while (ch < '0' || ch > '9') ch = getchar(); while (ch >= '0' && ch <= '9') x = x * 10 + ch - '0', ch = getchar ( ); } else { T _read_flag = (T)(1); while (ch < '0' || ch > '9') _read_flag = ch == '-' ? -1 : 1, ch = getchar(); while (ch >= '0' && ch <= '9') x = x * 10 + ch - '0', ch = getchar ( ); x *= _read_flag; } return void(); }
template <typename T> inline void read(vector<T> &v) { for (T &i : v) read(v); }
template <typename T, typename... Args> inline void read(T &x, Args&... args) { read(x), read(args...); }
template <typename T, typename U> inline void read(pair<T, U> &p) { read(p.first, p.second); }
template <typename T, typename U, typename V> inline void read(tuple<T, U, V> &t) { read(get<0>(t), get<1>(t), get<2>(t)); }
inline void write ( char c ) { putchar ( c ); }
inline void write ( string s ) { for (char c : s) putchar ( c ); }
template <typename T> inline void write(T x, bool is_unsigned = false) { if (!is_unsigned) if (x < 0) x = -x, putchar ('-'); if (x > 9) write(x / 10); putchar (x % 10 ^ '0'); }
template <typename T> inline void writeln(T x) { write (x), putchar('\n'); }
template <typename T> inline void writespc(T x) { write (x), putchar(' '); }
template <typename T, typename ... Args> inline void write(T x, Args ... args) { write(x), write(args...); }
template <typename T, typename ... Args> inline void writeln(T x, Args ... args) { write(x), putchar(' '), write(args...), putchar('\n'); }
template <typename T, typename ... Args> inline void writespc(T x, Args ... args) { write(x), putchar(' '), write(args...), putchar(' '); }
} // namespace easy_IO
using namespace easy_IO;

signed main() {
	// ios_base ::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
	int T;
	read(T);
	auto slv = [&]() {
		constexpr int N = 1 << 10;
		int n, m;
		read(n, m);
		bitset<N> f[2][N];
		f[0][0][0] = 1;
		rep(i, 1, n, v, w)  {
			read(v, w);
			rep(j, 0, N - 1)
				f[i & 1][j ^ w] |= f[(i & 1) ^ 1][j] << v;
		}
		int ans = -1;
		rep(i, 0, N - 1) 
			if (f[(n + 1) % 2][i][m]) ans = i;
		writeln(ans);
	};
	while (T--)slv();

#if defined(LOCAL) && !defined(CPH)
	std::cerr << "Spend Time : " << clock() * 1. / CLOCKS_PER_SEC * 1e3 << " ms \n";
#endif
	return 0;
}