#include <bits/stdc++.h>
using namespace std;
int n,m;
int fa[1001]={0};
int Find_set(int x)
{
    if(fa[x]!=x)
    {
        fa[x]=Find_set(fa[x]);
    } 
    return fa[x];
}
void Make_set(int x,int y)
{
    int px=Find_set(x);
    int py=Find_set(y);
    if(px!=py)
    {
        fa[px]=py;
    }
 } 
struct node
{
    int x,y,t;
}a[100001];
bool cmp(node x,node y)
{
    return x.t<y.t; 
} 
int main()
{
   freopen("roada.in","r",stdin);
   freopen("roada.out","w",stdout);
      cin>>n>>m;
      for(int i=1;i<=m;i++)
      {
          cin>>a[i].x>>a[i].y>>a[i].t;
      }
      for(int j=1;j<=n;j++)fa[j]=j;
      sort(a+1,a+1+m,cmp);
      int ans=0;
      for(int i=1;i<=m;i++)
      {
          if(Find_set(a[i].x)!=Find_set(a[i].y))
          {
              ans=max(ans,a[i].t);
              Make_set(a[i].x,a[i].y);
          }
      }
      for(int i=2;i<=n;i++)
      {
          if(Find_set(i-1)!=Find_set(i))
          {
              cout<<-1<<endl;
              return 0;
          }
      }
      cout<<ans<<endl;
      return 0;
}