#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 fa[U], siz[U];
int find(int e)
{
    if (fa[e] == e) return e;
    return fa[e] = find(fa[e]);
}
void merge(int u, int v)
{
    siz[find(u)] += siz[find(v)];
    fa[find(v)] = find(u);
}
int head[U], nxt[U], to[U], val[U], tot;
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); }

    int ans = 0;
    rep(b, 0, 30)
    {
        hrp(i, 1, n) fa[i] = i, fa[i+n] = i+n, siz[i] = 1;
        hrp(x, 1, n) for(int i = head[x]; i; i = nxt[i])
        {
            int y = to[i], z = val[i];

            if ((z>>b)&1)
            {
                if (find(x) == find(y) || find(x+n) == find(y+n)) return cout<<-1<<endl, 0;
                merge(x, y+n); merge(x+n, y);
            }
            else
            {
                if (find(x) == find(y+n) || find(x+n) == find(y)) return cout<<-1<<endl, 0;
                merge(x, y); merge(x+n, y+n);
            }
        }
        hrp(i, 1, n)
        {
            ans += min(siz[find(i)], siz[find(i+n)])*(1<<b);
            siz[find(i)] = siz[find(i+n)] = 0;
        }
    }

    cout<<ans<<endl;
    
    return 0;
}
/*
4 2
1 2 3
2 3 6
 */