#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);
	{
		atcoder::dsu uf(n);
		for(int i=0;i<m;i++){
			cin>>u[i]>>v[i]>>h[i];
			u[i]--;v[i]--;
			uf.merge(u[i],v[i]);
		}
		if(!uf.same(0,n-1)){
			cout<<"NaN"<<endl;
			return 0;
		}
	}
	int l=1,r=2e9;
	while(l+1<r){
		int c=(l+r)/2;
		atcoder::dsu uf(n);
		for(int i=0;i<m;i++)if(c<=h[i])uf.merge(u[i],v[i]);
		if(uf.same(0,n-1))l=c;
		else r=c;
	}
	cout<<l<<endl;
}