#include<bits/stdc++.h>//码风不好，请见谅
using namespace std;
#define endl '\n'
#define ll long long
const int N=2e5+10;
struct EDGE
{
	int x,y,d;
}edge[N];
int book[N],du[N],n,m,fa[N],s[N],t[N];
bool cmp(EDGE a,EDGE b)
{
	return a.d<b.d;
}
int find(int x)
{
	if(fa[x]==x)return x;
	else return fa[x]=find(fa[x]);
}
vector<int>v[N];
bool check(int f)
{
	for(int i=1;i<=(n<<1);i++)//初始化+清空
	{
		s[i]=t[i]=0;
		book[i]=0;
		fa[i]=i;
		v[i].clear();
	}
	for(int i=1;i<=f;i++)//建图
	{
		v[edge[i].x].push_back(edge[i].y+n);
		v[edge[i].y+n].push_back(edge[i].x);
		fa[find(edge[i].x)]=find(edge[i].y+n);//并查集
	}
	queue<int>q;
	for(int i=1;i<=n;i++)//为下面的删边初始化
	{
		if(v[i].size()==1)
		{
			q.push(i);
		}
		if(v[i+n].size()==1)
		{
			q.push(i+n);
		}
		du[i]=v[i].size();
		du[i+n]=v[i+n].size();
	}
	while(!q.empty())//删边
	{
		int u=q.front(),k=0;
		q.pop();
		if(book[u])continue;
		for(int i=0;i<v[u].size();i++)
		{
			int vv=v[u][i];
			if(!book[vv])
			{
				du[vv]--;
				k=vv;
				break;
			}
		}
		if(!k)continue;
		book[u]=1;
		book[k]=1;
		u=k;
		for(int i=0;i<v[u].size();i++)
		{
			int vv=v[u][i];
			du[vv]--;
			if(du[vv]==1)
			{
				q.push(vv);
			}
		}
	}
	for(int i=1;i<=(n<<1);i++)
	{
		if(!(book[i]|du[i]))
		{
			return 0;
		}
	}
	for(int i=1;i<=n;i++)
	{
		s[find(i)]++;
	}
	for(int i=1+n;i<=n+n;i++)
	{
		t[find(i)]++;
	}
	for(int i=1;i<=(n<<1);i++)
	{
		if(s[i]!=t[i])return 0;
	}
	return 1;
}
int main()
{
	ios::sync_with_stdio(0);
	cin.tie(NULL);cout.tie(NULL);
	cin>>n>>m;
	for(int i=1;i<=m;i++)cin>>edge[i].x>>edge[i].y>>edge[i].d;
	sort(edge+1,edge+m+1,cmp);//排序
	int l=1,r=m,ans=-1;//二分
	while(l<=r)
	{
		int mid=l+r>>1;
		if(check(mid))
		{
			r=mid-1;
			ans=edge[mid].d;
		}
		else l=mid+1;
	}
	cout<<ans;
	return 0;
}