#include <cstdio>
#include <vector>
using namespace std;
typedef long long LL;
struct DSU {
	vector <int> pa, dist;
	DSU(int size) {
		pa.resize(size + 1), dist.resize(size + 1, 0);
		for (int i = 1; i <= size; ++i) pa[i] = i;
	}
	~DSU() {}

	int query(int u) {
		int cnt = 0, _u = u;
		while (pa[u] != u) cnt ^= dist[u], u = pa[u];
		dist[_u] = cnt, pa[_u] = u;
		return u;
	}

	bool merge(int u, int v, int w) {
		int pu = query(u), pv = query(v);
		if (pu == pv) {
			if (dist[u] ^ dist[v] ^ w) return false;
			return true;
		}
		pa[pu] = pv, dist[pu] = dist[u] ^ dist[v] ^ w;
		return true;
	}
};
const int N = 1e5 + 5;
int com[30][N], diff[30][N];
bool is_rt[N];
int main() {
	int n, m;
	scanf("%d%d", &n, &m);
	DSU dsu(n);
	for (int i = 1; i <= m; ++i) {
		int u, v, w;
		scanf("%d%d%d", &u, &v, &w);
		if (!dsu.merge(u, v, w)) {
			printf("-1\n");
			return 0;
		}
	}
	for (int u = 1; u <= n; ++u) is_rt[u] = false;
	for (int u = 1; u <= n; ++u) {
		int pu = dsu.query(u);
		is_rt[pu] = true;
		for (int step = 0; step < 30; ++step) {
			if ((dsu.dist[u] >> step) & 1) diff[step][pu]++;
			else com[step][pu]++;
		}
	}
	LL ans = 0;
	for (int u = 1; u <= n; ++u) {
		if (is_rt[u])
			for (int step = 0; step < 30; ++step)
				ans += (1ll * min(diff[step][u], com[step][u])) << step;
	}
	printf("%lld", ans);
	return 0;
}