#include<bits/stdc++.h>

#define int long long
#define ll long long
using namespace std;

const int N = 500005;
int n, m;
int a[N];
ll trie[20000005][2];
ll tot;
ll siz[20000005];

struct dat{
	ll sum;
	int id, rk;
	friend bool operator<(dat xx, dat yy)
	{
		return xx.sum < yy.sum;
	}
};

void insert(ll x)
{
	int p = 0;//这个节点拒绝装载任何信息
	for(int i = 31; i >= 0; i --)
	{
		int t = (x >> i) & 1ll;
		siz[p] ++;
		if(!trie[p][t])
		{
			trie[p][t] = ++tot;
		}
		p = trie[p][t];

	}
	siz[p] ++;//子树大小
}
ll query(ll x, int rk)
{
	int p = 0;
	ll res = 0;
	for(int i = 31; i >= 0; i --)
	{
		int t = (x >> i) & 1ll;
		if(!trie[p][!t])
		{
			p = trie[p][t];
		}
		else if(siz[trie[p][!t]] < rk)//否则只能去相同地方 一定有
		{
			p = trie[p][t];
			rk -= siz[trie[p][!t]];
		}
		else
		{
			p = trie[p][!t];
			res |= (1ll << i);
		}
	}
	return res;
}
priority_queue<dat> q;

signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
//	cout << (1ll << 32) - 1 << endl;return 0;//共32位
	cin >> n >> m;
	m *= 2;
	for(int i = 1; i <= n; i ++)
	{
		cin >> a[i];
		a[i] ^= a[i - 1];
	}
	for(int i = 0; i <= n; i ++)
	{
		insert(a[i]);
	}
	for(int i = 0; i <= n; i ++)
	{
		q.push({query(a[i], 1), i, 1});
	}
	ll ans = 0;
	for(int i = 1; i <= m; i ++)
	{
		dat u = q.top();
		q.pop();
		ans += u.sum;
		if(u.rk >= n)continue;
		u.rk ++;
		u.sum = query(a[u.id], u.rk);
		q.push(u);
	}
	cout << ans / 2 << endl;


	return 0;

}