#include <bits/stdc++.h>
using namespace std;
const int N = 3e5 + 10;
#define ll long long
struct e {
    int u,v,w;
}e[N];
int f[N],siz[N],n,m;

void init() {
    for (int i = 1;i <= n;++i) f[i] = i,f[i+n] = i+n,siz[i] = 1,siz[i+n] = 0;
}
int find(int x) {
    //cout << x;
    return x == f[x] ? x : f[x] = find(f[x]);
}

void merge(int x,int y) {
    if (x == y) return ;
    siz[y] += siz[x];siz[x] = 0;f[x] = y;
}

signed main() {
    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    cin >> n >> m;
    for (int i = 1;i <= m;++i) {
        cin >> e[i].u >> e[i].v >> e[i].w;
    }
    bool flag = 0;
    ll ans = 0;
    for (int i = 0;i < 30;++i) {
        init();
        for (int j = 1;j <= m;++j) {
            //for (int k = 1;k <= n;++k )printf("%d %d\n",siz[find(k)],siz[find(k+n)]);
            int nowval = (e[j].w >> i) & 1;
            int x = find(e[j].u),y = find(e[j].v);
            int xx = find(e[j].u+n),yy = find(e[j].v+n);
            if (nowval) {
                if (find(e[j].u) == find(e[j].v)) {
                    flag = 1;break;
                }
                merge(x,yy);merge(y,xx);
            } else {
                if (find(e[j].u) == find(e[j].u+n)) {
                    flag = 1;break;
                }
                merge(x,y);merge(xx,yy);
            }
        }
            //for (int k = 1;k <= n;++k )printf("%d %d\n",siz[find(k)],siz[find(k+n)]);
        for (int j = 1;j <= n;++j) {
            //printf("wq;%d %d\n",siz[find(j)],siz[find(j+n)]);
            if (find(j) != find(j+n)) {
                ans += (ll)min(siz[find(j)],siz[find(j+n)]) * (1LL << i);
                siz[find(j)] = siz[find(j+n)] = 0;
            } else {
                flag = 1;
                break;
            }
        }
        if (flag) break;
    }
    if (flag)     cout << -1;
    else cout << ans;
}