#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
int g[222][222], d[222][222], v[222], p[222], f[222], n, m, x, y, z;
void work(int u, int v) {
  vector<pair<int, int> > a, b;
  for (int i = 1; i <= n; ++i) {
    a.push_back(make_pair(d[u][i], d[v][i]));
  }
  sort(a.begin(), a.end());
  int tt = ((int)a.size()), d = INF;
  for (int i = 0; i < tt; ++i) {
    while (((int)b.size()) && b.back().second <= a[i].second) b.pop_back();
    b.push_back(a[i]);
  }
  if (b.size() == 1)
    if (b[0].first < b[0].second)
      d = b[0].first << 1;
    else
      d = b[0].second << 1;
  tt = ((int)b.size());
  for (int i = 1; i < tt; ++i)
    d = min(d, g[u][v] + b[i - 1].first + b[i].second);
  z = min(z, d);
}
int main() {
  scanf("%d%d", &n, &m);
  memset(g, INF, sizeof(g));
  for (int i = 0; i < m; i++) {
    scanf("%d %d %d", &x, &y, &z);
    z *= 2;
    g[x][y] = g[y][x] = min(g[x][y], z);
  }
  for (int i = 1; i <= n; i++) g[i][i] = 0;
  memcpy(d, g, sizeof d);
  for (int k = 1; k <= n; k++)
    for (int i = 1; i <= n; i++)
      for (int j = 1; j <= n; j++) d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
  z = 0x3f3f3f3f;
  for (int i = 1; i <= n; i++)
    for (int j = i; j <= n; j++)
      if (g[i][j] < 0x3f3f3f3f) work(i, j);
  printf("%.2lf\n", z / 4.0);
  return 0;
}
