#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9 + 7;
int n, m;
int adj[205][205];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> m;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      adj[i][j] = INF;
    }
    adj[i][i] = 0;
  }
  for (int i = 1; i <= m; i++) {
    int u, v, w;
    cin >> u >> v >> w;
    adj[u][v] = adj[v][u] = w;
  }
  for (int k = 1; k <= n; k++) {
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j <= n; j++) {
        adj[i][j] = min(adj[i][j], adj[i][k] + adj[k][j]);
      }
    }
  }
  int ans = INF;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      if (i == j) continue;
      pair<int, int> d[n + 5];
      for (int k = 1; k <= n; k++) {
        d[k] = {adj[i][k], k};
      }
      sort(d + 1, d + 1 + n, greater<pair<int, int>>());
      int last = d[1].second;
      ans = min(ans, adj[i][last] * 2);
      for (int k = 2; k <= n; k++) {
        int cur = d[k].second;
        if (adj[j][cur] > adj[j][last]) {
          ans = min(ans, adj[i][cur] + adj[j][last] + adj[i][j]);
          last = cur;
        }
      }
    }
  }
  cout << ans / 2 << "." << (ans & 1 ? "500000" : "000000") << "\n";
  return 0;
}
