#include <bits/stdc++.h>
using namespace std;
using ll=long long;
#include <atcoder/dsu>
int main(){
	int n,m;
	cin>>n>>m;
	vector<int> u(m),v(m),h(m);
	for(int i=0;i<m;i++)cin>>u[i]>>v[i]>>h[i],u[i]--,v[i]--;
	vector<int> idx(m);
	iota(idx.begin(),idx.end(),0);
	ranges::sort(idx,greater{},[&](int i)->int{
		return h[i];
	});
	atcoder::dsu uf(n);
	for(int i:idx){
		uf.merge(u[i],v[i]);
		if(uf.same(0,n-1)){
			cout<<h[i]<<endl;
			return 0;
		}
	}
	cout<<"NaN"<<endl;
		
}