//written by Amekawa_kanade
#include<bits/stdc++.h>
using namespace std;
void syncoff()//fuck you sync
{
    ios::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
}
#define endl '\n'
const int N=5e5+11;
using ll=long long;
using i128=__int128;
using ld=long double;
const ll JT=998244353;
const ll GEH=1e9+7;
const ll ZLH=1e9+9;
int t,n,k,m,q;
vector<pair<int,int> > G[N];
int c0,c1,qaq[N];
void clr_g()
{
	for(int i=1;i<=n;++i)  G[i].clear(),qaq[i]=0;
	c0=0,c1=0;
}
bool dfs(int u,int val)
{
	if(qaq[u])
	{
		if(qaq[u]!=val) return 1;
		else return 0;
	}
	qaq[u]=val;bool ret=0;
	if(val==1) ++c0;else ++c1;
	for(auto [v,x]:G[u])
	{
		if(x) ret|=dfs(v,-val);
		else ret|=dfs(v,val);
	}
	return ret;
}
ll ans;
struct cstrs
{
	int u,v,w;
}EG[N];
void clr()
{
	for(int i=1;i<=m;++i) EG[i]={0,0,0};
	ans=0;clr_g();
}
void solve()
{
	cin>>n>>m;
	for(int i=1;i<=m;++i)
	{
		cin>>EG[i].u>>EG[i].v>>EG[i].w;
	}
	bool ok=1;
	for(int p=30;ok&&p>=0;--p)
	{
		clr_g();
		for(int i=1;i<=m;++i)
		{
			int u=EG[i].u,v=EG[i].v;
			int pw=(EG[i].w>>p)&1;
			if(pw) G[u].push_back(make_pair(v,1)),G[v].push_back(make_pair(u,1));
			else G[u].push_back(make_pair(v,0)),G[v].push_back(make_pair(u,0));
		}
		for(int i=1;i<=n;++i) if(!qaq[i])
		{
			ok=(!dfs(i,1));if(!ok) break;
			ans+=(1<<p)*min(c0,c1);
			c0=c1=0;
		}
	}
	if(!ok)
	{
		cout<<-1<<endl;return clr();
	}
	cout<<ans<<endl;
	return clr();
}
int main()
{
 	t=1;
    //cin>>t;
    while(t--) solve();
    return 0;
}