#include <bits/stdc++.h>
using namespace std;
#if __has_include("all.hpp")
#include "all.hpp"
#else
#include <atcoder/all>
#endif
using namespace atcoder;
int main(void){
    int n,m;
    cin>>n>>m;
    vector<pair<int,pair<int,int>>>v;
    for(int i=0;i<m;i++){
        int a,b,h;
        cin>>a>>b>>h;
        v.push_back({h,{a-1,b-1}});
    }
    sort(v.begin(),v.end());
    reverse(v.begin(),v.end());
    dsu d(n);
    for(int i=0;i<m;i++){
        d.merge(v[i].second.first,v[i].second.second);
        if(d.same(0, n-1)){
            cout<<v[i].first<<endl;
            return 0;
        }
    }
    cout<<"NaN"<<endl;
    return 0;
}