#include<bits/stdc++.h>
#define debug(x) cerr<<#x<<":"<<x<<'\n'
#define eb emplace_back
using namespace std;
using ll = long long;
using pii = pair <int,int>;
using pll = pair <ll,ll>;
const int N = 1e5 + 5, MOD = 1e9 + 7;
bool st[32][N];
int n, m, c[32][N];
ll ans, a[N];
vector <vector<pii>> e[32];
bool dfs(int u,int bit,int fa)
{
	st[bit][u] = 1;
	for(auto son:e[bit][u])
	{
		int v = son.first, w = son.second;
		if(v!=fa)
		{
			if(c[bit][v]==-1)
			{
				if(w) c[bit][v] = (!c[bit][u]);
				else c[bit][v] = c[bit][u];
				if(!st[bit][v] && !dfs(v,bit,u)) return false;
			}
			else if((c[bit][v]^c[bit][u])!=w) return false;
		}
	}
	return true;
}
void solve()
{
	cin>>n>>m;
	for(int j=0;j<=30;j++){
		e[j].resize(n+1);
	}
	for(int i=1,u,v,w;i<=m;i++)
	{
		cin>>u>>v>>w;
		for(int j=0;j<=30;j++)
		{
			e[j][u].eb(v,(w>>j)&1);
			e[j][v].eb(u,(w>>j)&1);
		}
	}
	for(int bit=0;bit<=30;bit++)
	{
		pll res = {0,0};
		bool ck = 1;
		for(int i=1;i<=n;i++) c[bit][i] = -1;
		for(int i=1;i<=n;i++)
		{
			if(c[bit][i]==-1)
			{
				c[bit][i] = 0;
				if(!st[bit][i] && !dfs(i,bit,0))
				{
					ck = 0;
					break;
				}
			}
		}
		ll sum = 1e18;
		if(ck)
		{
			for(int i=1;i<=n;i++)
			{
				res.first += (1ll<<bit)*c[bit][i];
				res.second += (1ll<<bit)*(!c[bit][i]);
			} 
			sum = min(res.first,res.second);
		} 
		else
		{
			cout<<-1;
			return ;
		}
		ans += sum;
	}
	cout<<ans;
}
int main(void)
{
	ios::sync_with_stdio(0);
	cin.tie(0), cout.tie(0);
	int T = 1;
	// cin >> T;
	while(T--) solve();
	return 0;
}