#include<bits/stdc++.h>

using namespace std;
#define int long long

const int mod = 998244353;

bool dfs(int u, vector<int> &color, vector<vector<int>> &g, vector<vector<int>> &g1, int &x, int &y) {
    for (auto v: g[u]) {
        if (color[v] == 0) {
            color[v] = color[u];
            if (color[v] == 1) x++;
            else y++;
            if (!dfs(v, color, g, g1, x, y)) return false;
        } else if (color[u] != color[v]) return false;
    }
    for (auto v: g1[u]) {
        if (color[v] == 0) {
            if (color[u] == 1) y++, color[v] = -1;
            else x++, color[v] = 1;
            if (!dfs(v, color, g, g1, x, y)) return false;
        } else if (color[u] == color[v]) return false;
    }
    return true;
}

void solve() {
    int n, m;
    cin >> n >> m;
    vector<array<int, 3>> re(m);
    for (int i = 0; i < m; i++) {
        cin >> re[i][0] >> re[i][1] >> re[i][2];
        re[i][0]--, re[i][1]--;
    }
    int res = 0;
    for (int i = 0; i < 30; i++) {
        vector<vector<int>> g(n), g1(n);
        vector<int> color(n);
        vector<pair<int, int>> ans;
        for (int j = 0; j < m; j++)
            if (re[j][2] & (1 << i))
                g1[re[j][0]].push_back(re[j][1]), g1[re[j][1]].push_back(re[j][0]);
            else
                g[re[j][0]].push_back(re[j][1]), g[re[j][1]].push_back(re[j][0]);
        for (int j = 0; j < n; j++) {
            if (color[j]) continue;
            int x = 1, y = 0;
            color[j] = 1;
            if (!dfs(j, color, g, g1, x, y)) {
                cout << "-1\n";
                return;
            }
            ans.emplace_back(x, y);
        }
        for (auto [x, y]: ans) res += min(x, y) * (1 << i);
    }
    cout << res << "\n";
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t = 1;
//    cin >> t;
    while (t--) solve();
}