#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define ll long long
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define repl(i,a,b) for(ll i=(a);i<(b);i++)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()

template <typename T> bool chmin(T &a,T b){if(a>b){a=b;return true;} return false;}
template <typename T> bool chmax(T &a,T b){if(a<b){a=b;return true;} return false;}


int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int n,m; cin >> n >> m;
  vector<tuple<int,int,ll>> e;
  rep(i,0,m){
    int u,v,h; cin >> u >> v >> h;
    u--,v--;
    e.push_back({u,v,h});
  }
  ll ok=0,ng=2e9;
  while(ng-ok>1){
    int mid=(ok+ng)/2;
    dsu d(n);
    for(auto [u,v,h]:e){
      if(h>=mid){
        d.merge(u,v);
      }
    }
    if(d.same(0,n-1)) ok=mid;
    else ng=mid;
  }
  if(ok == 0) cout << "NaN" << "\n";
  else cout << ok << "\n";
}