#include <cstdio>
#include <vector>
#include <iostream>
using namespace std;
const int N = 1e5 + 5;
struct DSU {
	int pa[N], h[N], diff[N], com[N], dist[N], vis[N], sz;

	DSU(int size) {
		for (int i = 1; i <= size; ++i) pa[i] = i, h[i] = 0, dist[i] = 0, com[i] = 1, diff[i] = 0, vis[i] = 0;
		sz = size;
	}
	~DSU() {}

	void init() {
		for (int i = 1; i <= sz; ++i) pa[i] = i, h[i] = 0, dist[i] = 0, com[i] = 1, diff[i] = 0, vis[i] = 0;
	}

	int qry(int x) {
		int cnt = 0, x_ = x;
		while (pa[x] != x) cnt += dist[x], x = pa[x];
		dist[x_] = cnt, pa[x_] = x;
		return x;
	}

	bool merge(int x, int y, int op) {
		int rtx = qry(x), rty = qry(y);
		if (rtx == rty) {
			if ((dist[x] + dist[y]) % 2 == op) return true;
			// cerr << x << ' ' << dist[x] << ' ' << y << ' ' << dist[y] << ' ' << op << '\n';
			return false;
		}
		if (h[rtx] > h[rty]) swap(rtx, rty);
		pa[rtx] = rty;
		h[rtx] = max(h[rtx], h[rty] + 1);
		if ((dist[x] + dist[y]) % 2 == op) dist[rtx] = 0, com[rty] += com[rtx], diff[rty] += diff[rtx];
		else dist[rtx] = 1, diff[rty] += com[rtx], com[rty] += diff[rtx];
		return true;
	}
};
const int M = 2e5 + 5;
struct Data {
	int u, v, w;
} a[M];
typedef long long LL;
LL solve(DSU &dsu, int step, int m) {
	dsu.init();
	for (int i = 1; i <= m; ++i) {
		int u = a[i].u, v = a[i].v, w = a[i].w;
		int flag = 1;
		if (w & (1 << step)) flag = 1;
		else flag = 0;
		if (!dsu.merge(u, v, flag)) {
			// cerr << step << '\n';
			return -1;
		}
	}
	LL ans = 0;
	for (int i = 1; i < dsu.sz; ++i) {
		int rti = dsu.qry(i);
		if (dsu.vis[rti]) continue;
		else dsu.vis[rti] = 1, ans += min(dsu.com[rti], dsu.diff[rti]);
	}
	return (ans << step);
}
int main() {
	int n, m;
	scanf("%d%d", &n, &m);
	DSU dsu(n);
	for (int i = 1; i <= m; ++i) {
		scanf("%d%d%d", &a[i].u, &a[i].v, &a[i].w);
	}

	LL ans = 0;
	for (int i = 0; i < 30; ++i) {
		LL res = solve(dsu, i, m);
		if (res == -1) {
			printf("-1\n");
			return 0;
		}
		ans += res;
	}

	printf("%lld\n", ans);
	return 0;
}