#include <bits/stdc++.h>
using namespace std;
    
#define int long long
#define pb push_back
#define ub upper_bound
#define lb upper_bound
#define mp make_pair
#define F first
#define S second
#define FOR(i,a,b) for(int (i)=(a);(i)<(b);(i)++)
#define rep(i,n) FOR(i,0,n)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define SORT(c) sort((c).begin(),(c).end())
#define ve vector
#define vi vector<int>
#define vp vector<pair<int,int>>
#define vvi vector<vector<int>>
    
using ll = long long;
const ll INF = LLONG_MAX / 40 - 100;
ll mod = 1e9 + 7;
int dx[] = {-1,0,1,0}, dy[] = {0,1,0,-1};
int ddx[] = {-1,0,1,-1,1,-1,0,1}, ddy[] = {1,1,1,0,0,-1,-1,-1};
vector<ll> prime;
    
class fact {
public:
    int fmod = 1e9+7;
    vector<int> fac, inv;
    fact (int n, int Mod = 1e9+7) {
        fmod = Mod;
        fac = vector<int>(n + 1,0);
        inv = vector<int>(n + 1,0);
        fac[0] = 1; for (int i = 1; i < n + 1; i++) fac[i] = fac[i-1] * i % fmod;
        for (int i = 0;i < n + 1;i++) inv[i] = fact::POW(fac[i],fmod-2);
    }
    ll nCr(ll n, ll r) {if (n<r) return 0; return (fac[n] * inv[r] % fmod) * inv[n-r] % fmod;}
    ll POW(ll a, ll b) {ll c = 1; while (b > 0) {if (b & 1) {c = a * c%fmod;}a = a * a%fmod; b >>= 1;}return c;}
};
    
template <class T = ll> T in() {T x; cin >> x; return (x);}
void DEBUG(vector<int> a) {for(int i=0;i<a.size();i++)cout<<a[i]<<" ";cout<<endl;}
void EMP(int x) {cout<<"!!!"<<x<<"!!!"<<endl;}
ll GCD(ll a, ll b) {ll c; while (b != 0) {c = a % b; a = b; b = c;}return a;}
ll LCM(ll a, ll b) {return (a / GCD(a,b)) * b;}
ll POW(ll a, ll b) {ll c = 1; while (b > 0) {if (b & 1) {c = a * c%mod;}a = a * a%mod; b >>= 1;}return c;}
void PRI(ll n) {bool a[n + 1LL]; for (int i = 0; i < n + 1LL; i++) {a[i] = 1LL;}for (int i = 2; i < n + 1LL; i++) {if (a[i]) {prime.pb(i); ll b = i; while (b <= n) {a[b] = 0; b += i;}}}}
template <typename T> T chmin(T& a, T b) {if(a>b)a=b;return a;}
template <typename T> T chmax(T& a, T b) {if(a<b)a=b;return b;}
bool isSqrt(ll a) {return pow(sqrt(a),2) == a ? 1 : 0;}
void YesNo(bool a) {if (a) cout << "Yes"; else cout << "No"; cout << endl;}
void yesno(bool a) {if (a) cout << "yes"; else cout << "no"; cout << endl;}
void YESNO(bool a) {if (a) cout << "YES"; else cout << "NO"; cout << endl;}

long long extGCD(long long a, long long b, long long &x, long long &y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }
    long long d = extGCD(b, a % b, y, x);
    y -= a / b * x;
    return d;
}

long long mul(long long a, long long b, long long mod) {
    long long keta[20] = {};
    long long c = b;
    long long now = 0;
    while (c != 0ll) {
        keta[now] = c % 10; c /= 10; now++;
    }
    long long res = 0;
    for (int i = 19; i >= 0; --i) {
        res *= 10; res %= mod;
        res += keta[i] * a % mod;
    }
    return res % mod;
}

class BIT {
public:
    vector<int> bit;
    int n;
    BIT(int x) : n(x), bit(vector<int>(x + 1)) {}

    void add(int i, int w) {
        ++i;
        for (int x = i; x <= n; x += (x & -x)) bit[x] += w;
    }

    int sum(int i) {
        ++i;
        int ret = 0;
        for (int x = i; x > 0; x -= (x & -x)) ret += bit[x];
        return ret;
    }
};

void solve() {
    int n, k; cin >> n >> k;
    vector<int> a(n); rep (i, n) cin >> a[i];
    vector<int> ruiseki(n + 1);
    rep (i, n) ruiseki[i + 1] = ruiseki[i] ^ a[i];
    sort(all(ruiseki));

    BIT bit(1100000);
    rep (i, n + 1) bit.add(ruiseki[i], 1);

    int l = -1, r = (1 << 20);
    while (r - l > 1) {
        int mid = (r + l) / 2;
        int tmp = 0;
        rep (i, n + 1) {
            rep (j, 20) {
                if (!((mid >> 19 - j) & 1)) {
                    int mokuhyou = ((mid >> 19 - j) << 19 - j) + (1 << 19 - j);
                    int Akai = (ruiseki[i] >> 19 - j) << 19 - j;
                    int Bkagen = mokuhyou ^ Akai;
                    int Bzyougen = Bkagen + (1 << 19 - j);
                    // cout << mid << " " << mokuhyou << " " << ruiseki[i] << " " << Akai << " ";
                    tmp += bit.sum(Bzyougen - 1) - bit.sum(Bkagen - 1);
                    // cout << bit.sum(Bzyougen - 1) << " " << bit.sum(Bkagen) << endl;
                }
            }
            tmp += bit.sum(ruiseki[i] ^ mid) - bit.sum((ruiseki[i] ^ mid) - 1);
        }
        if (mid == 0) tmp -= n;
        tmp /= 2;
        if (mid == 0) tmp += n;
        // if (mid == 7) cout << tmp << endl;
        if (tmp >= k) l = mid;
        else r = mid;
    }
    cout << l << endl;
    return;
}

signed main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();    
}




Measured memory_bytes: 13096