#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define RFOR(i, a, b) for (int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;

const int INF = 1000'474'747;
const int N = 25;
int dp[1 << N];
bool ok[1 << N];

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout << fixed << setprecision(15);
	
	int n;
	cin >> n;
	VI a(n);
	FOR (i, 0, n)
		cin >> a[i];
	
	FOR (i, 0, n)
	{
		FOR (j, i + 1, n)
		{
			FOR (k, j + 1, n)
			{
				if ((a[i] ^ a[j] ^ a[k]) == 0)
					ok[(1 << i) + (1 << j) + (1 << k)] = 1;
			}
		}
	}
	FOR (mask, 0, 1 << n)
	{
		FOR (i, 0, n)
		{
			if (mask & (1 << i))
				ok[mask] |= ok[mask ^ (1 << i)];
		}
	}
	
	FOR (i, 0, 1 << n)
	{
		if (ok[i])
			dp[i] = INF;
	}
	FOR (mask, 0, 1 << n)
	{
		if (!ok[mask])
			continue;
		FOR (i, 0, n)
		{
			if (mask & (1 << i))
				dp[mask] = min(dp[mask], dp[mask ^ (1 << i)] + 1);
		}
	}
	cout << dp[(1 << n) - 1] << '\n';
	
	
	cerr << double(clock()) / CLOCKS_PER_SEC << '\n';
	
	return 0;
}