#include <bits/stdc++.h>
#ifdef LOCAL
#include <debug.hpp>
#else
#define debug(...) void(0)
#endif

#include "datastructure/UnionFind.hpp"

using namespace std;

typedef long long ll;
#define all(x) begin(x), end(x)
constexpr int INF = (1 << 30) - 1;
constexpr long long IINF = (1LL << 60) - 1;
constexpr int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};

template <class T> istream& operator>>(istream& is, vector<T>& v) {
    for (auto& x : v) is >> x;
    return is;
}

template <class T> ostream& operator<<(ostream& os, const vector<T>& v) {
    auto sep = "";
    for (const auto& x : v) os << exchange(sep, " ") << x;
    return os;
}

template <class T, class U = T> bool chmin(T& x, U&& y) { return y < x and (x = forward<U>(y), true); }

template <class T, class U = T> bool chmax(T& x, U&& y) { return x < y and (x = forward<U>(y), true); }

template <class T> void mkuni(vector<T>& v) {
    sort(begin(v), end(v));
    v.erase(unique(begin(v), end(v)), end(v));
}

template <class T> int lwb(const vector<T>& v, const T& x) { return lower_bound(begin(v), end(v), x) - begin(v); }

struct edge {
    int u, v, w;
    edge(int u, int v, int w) : u(u), v(v), w(w) {}
    bool operator<(const edge& rhs) const { return w < rhs.w; }
};

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, m;
    cin >> n >> m;
    vector<edge> es;
    for (int i = 0; i < m; i++) {
        int u, v, w;
        cin >> u >> v >> w;
        es.emplace_back(--u, --v, w);
    }

    sort(begin(es), end(es));
    UnionFind UF(n);
    int border = -1, threshold = -1;
    vector<vector<pair<int, int>>> G(n);
    for (int i = 0; i < m; i++) {
        auto [u, v, w] = es[i];
        UF.merge(u, v);
        G[u].emplace_back(v, w);
        G[v].emplace_back(u, w);
        if (UF.same(0, n - 1)) {
            border = i + 1;
            threshold = w;
            break;
        }
    }
    assert(border != -1);

    ll ans = IINF;
    {
        vector dp(n, vector<int>(2, INF));
        priority_queue<tuple<int, int, int>> pq;
        dp[0][0] = 0;
        pq.emplace(-dp[0][0], 0, 0);
        while (not pq.empty()) {
            auto [cost, v, x] = pq.top();
            pq.pop();
            cost *= -1;
            if (dp[v][x] != cost) continue;
            for (auto [u, w] : G[v]) {
                int nx = x, ncost = cost;
                if (x == 0 and w == threshold) {
                    nx++;
                } else
                    chmax(cost, w);
                if (chmin(dp[u][nx], ncost)) pq.emplace(-dp[u][nx], u, nx);
            }
        }
        ans = dp[n - 1][1] + threshold;
    }
    {
        auto calc = [&](int s) -> vector<int> {
            vector<int> dp(n, INF);
            priority_queue<pair<int, int>> pq;
            dp[s] = 0;
            pq.emplace(-dp[s], s);
            while (not pq.empty()) {
                auto [cost, v] = pq.top();
                pq.pop();
                cost *= -1;
                if (dp[v] != cost) continue;
                for (auto [u, w] : G[v]) {
                    if (chmin(dp[u], max(cost, w))) pq.emplace(-dp[u], u);
                }
            }
            return dp;
        };
        auto dp1 = calc(0), dp2 = calc(n - 1);
        for (int i = border; i < m; i++) {
            auto [u, v, w] = es[i];
            if (dp1[u] == INF) continue;
            if (dp2[v] == INF) continue;
            chmin(ans, w + max(dp1[u], dp2[v]));
        }
    }

    cout << ans << '\n';
    return 0;
}

answer.code:8:10: fatal error: datastructure/UnionFind.hpp: No such file or directory
    8 | #include "datastructure/UnionFind.hpp"
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.