#if __has_include(<yoniha/all.h>)
#include <yoniha/all.h>
using namespace atcoder;
#else
#include <bits/stdc++.h>
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
#endif
#endif
using namespace std;

#define int long long
#define all(x) (x).begin(), (x).end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rrep(i, n) for(int i = (int)((n) - 1); i >= 0; i--)
template <typename T> bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template <typename T> bool chmin(T &a,const T &b){if(a>b){a=b;return true;}return false;}

// using mint = modint;

signed main(){
  int n, m; cin >> n >> m;
  vector<tuple<int, int, int>> uvh(m);
  for(auto&& [u, v, h] : uvh) cin >> u >> v >> h, u--, v--;
  int ok = 0, ng = 1000000001;
  while(ng - ok > 1){
    int mid = (ok + ng) / 2;
    dsu d(n);
    for(auto [u, v, h] : uvh) if(h >= mid) d.merge(u, v);
    (d.same(0, n - 1) ? ok : ng) = mid;
  }
  if(ok == 0){
    println("NaN");
    return 0;
  }
  println("{}", ok);
}