#include<stdio.h>
int u[100005], v[100005], H[100005];
int h[100005], l;
int comp_h(int a, int b)
{
	if (H[h[a]] < H[h[b]])
		return 1;
	else
		return -1;
}
void swap_h(int a, int b)
{
	int f = h[a];
	h[a] = h[b];
	h[b] = f;
	return;
}
void push(int ne)
{
	h[l] = ne;
	int p = l++;
	for (; p > 0; p = (p - 1) / 2)
		if (comp_h((p - 1) / 2, p) > 0)
			swap_h((p - 1) / 2, p);
	return;
}
int pop()
{
	swap_h(0, --l);
	int p = 0;
	for (;;)
	{
		if (2 * p + 2 < l)
		{
			if (comp_h(2 * p + 1, 2 * p + 2) > 0)
			{
				if (comp_h(p, 2 * p + 2) > 0)
					swap_h(p, 2 * p + 2);
				p = 2 * p + 2;
			}
			else
			{
				if (comp_h(p, 2 * p + 1) > 0)
					swap_h(p, 2 * p + 1);
				p = 2 * p + 1;
			}
		}
		else if (2 * p + 1 < l)
		{
			if (comp_h(p, 2 * p + 1) > 0)
				swap_h(p, 2 * p + 1);
			p = 2 * p + 1;
		}
		else
			break;
	}
	return h[l];
}
int par[100005];
int root(int n)
{
	if (par[n] != n)
		par[n] = root(par[n]);
	return par[n];
}
void uni(int a, int b)
{
	a = root(a);
	b = root(b);
	par[a] = b;
	return;
}
int main()
{
	int n, m;
	scanf("%d %d", &n, &m);
	int i;
	for (i = 0; i < m; i++)
	{
		scanf("%d %d %d", &u[i], &v[i], &H[i]);
		u[i]--;
		v[i]--;
	}
	l = 0;
	for (i = 0; i < m; i++)
		push(i);
	for (i = 0; i < n; i++)
		par[i] = i;
	while (l > 0)
	{
		i = pop();
		uni(u[i], v[i]);
		if (root(0) != root(n - 1))
			continue;
		printf("%d\n", H[i]);
		return 0;
	}
	printf("NaN\n");
	return 0;
}