#define F_C
#include <bits/stdc++.h>
#define rep(i, l, r) for(int i = l; i < r; i++)
#define hrp(i, l, r) for(int i = l; i <= r; i++)
#define rev(i, r, l) for(int i = r; i >= l; i--)
#define int ll
using namespace std;
typedef long long ll;
template<typename tn = int> tn next(void) { tn k; cin>>k; return k; }
#ifndef LOCAL
#define D(...) 0
#endif
const int U = 5e5;
int head[U], nxt[U], to[U], val[U], tot;
int asu[U];
vector<int> cpn;
bool vis[U];
bool dfs(int e)
{
    if (vis[e]) return 1;
    vis[e] = 1;

    for(int i = head[e]; i; i = nxt[i])
    {
        int y = to[i], z = val[i];

        if (vis[y]) { if ((asu[y]^z) != asu[e]) return 0; }
        else
        {
            asu[y] = asu[e]^z;
            cpn.push_back(asu[y]);
            if (!dfs(y)) return 0;
        }
    }
    return 1;
}
void add(int x, int y, int z)
{
    to[++tot] = y; val[tot] = z; nxt[tot] = head[x]; head[x] = tot; 
}
signed main(void)
{
    #ifdef LOCAL
//	freopen("C:\\Users\\Loxil\\Desktop\\IN.txt", "r", stdin);
//	freopen("C:\\Users\\Loxil\\Desktop\\OUT.txt", "w", stdout);
    #endif
    
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    int n, m;
    cin>>n>>m;
    rep(i, 0, m) { int u, v, w; cin>>u>>v>>w; add(u, v, w); add(v, u, w); }

    int ans = 0;
    hrp(i, 1, n)
    {
        if (vis[i]) continue;

        cpn.clear();
        if (!dfs(i)) return cout<<-1<<endl, 0;

        rep(b, 0, 30)
        {
            int cnt1 = 0;
            for(auto v: cpn) cnt1 += (v>>b)&1;
            ans += (1<<b)*min(cnt1, (int)cpn.size()+1-cnt1);
        }
    }
    cout<<ans<<endl;
    
    return 0;
}
/*
4 2
1 2 3
2 3 6

3:4
2:2
1:1
 */