#include <bits/stdc++.h>
typedef long long ll;
struct To {
ll v, w;
ll i;
};
const ll inf = 1e15;
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
ll n, m;
std::cin >> n >> m;
std::vector<std::vector<To>> adj(n + 1);
std::vector<ll> roads(m);
for (ll i = 0, u, v, w; i < m; ++i) {
std::cin >> u >> v >> w;
adj[u].push_back({v, w, i});
adj[v].push_back({u, w, i});
roads[i] = w;
}
// exclude edge i
auto sssp = [&](ll i, ll add) {
std::vector<ll> ans(n + 1, inf);
std::vector<bool> vis(n + 1);
std::priority_queue<std::pair<ll, ll>> pq;
pq.push({0, 1});
while (!pq.empty()) {
auto [d, node] = pq.top();
d *= -1;
pq.pop();
if (vis[node]) {
continue;
}
vis[node] = true;
for (auto [ch, w, cur_i] : adj[node]) {
if (cur_i == i) {
w += add;
}
if (ans[ch] > d + w) {
ans[ch] = d + w;
pq.push({-ans[ch], ch});
}
}
}
return ans;
};
ll def = sssp(-1, 0)[n];
ll ans = def;
ll worst_road = roads[m - 1];
for (ll i = m - 2; i >= 0; --i) {
ans = std::max(ans, sssp(i, worst_road)[n]);
worst_road = std::max(worst_road, roads[i]);
}
std::cout << ans << '\n';
}
