#include <bits/stdc++.h>

using namespace std;

typedef pair<int, int> pii;
typedef long long ll;
const int N = 2000010, MOD = 998244353, INF = 0x3f3f3f3f;
int n, m, w[N];

int p[N];
int find(int x) { if (p[x] != x) p[x] = find(p[x]); return p[x]; }
void solve() {
    scanf("%d%d", &n, &m);
    iota(p, p + n + 1, 0);
    vector<array<int, 3> > v;
    for (int i = 1, a, b, c; i < m + 1; i++) {
        scanf("%d%d%d", &a, &b, &c);
        v.push_back({c, a, b});
    }
    sort(v.begin(), v.end());
    int res = INF;
    while (v.size() && find(1) != find(n)) {
        res = v.back()[0];
        int a = find(v.back()[1]), b = find(v.back()[2]);
        p[a] = b;
        v.pop_back();
    }
    if (find(1) == find(n)) printf("%d\n", res);
    else puts("NaN");
}

int main() {
    int T = 1;
    // cin >> T;
    while (T--) solve();
    return 0;
}