#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-7;
const int inf = 0x3f3f3f3f;
const int hinf = 0x3f3f3f3f;
const long long mod = 1000000007;
int n, m;
int dis[220][220];
int edge[40040][3];
vector<pair<int, int> > v;
pair<int, int> xulie[40040];
int main() {
  scanf("%d%d", &n, &m);
  int a, b, c;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) dis[i][j] = inf;
  for (int i = 1; i <= n; i++) dis[i][i] = 0;
  for (int i = 1; i <= m; i++) {
    scanf("%d%d%d", &a, &b, &c);
    dis[a][b] = dis[b][a] = c;
    edge[i][0] = a;
    edge[i][1] = b;
    edge[i][2] = c;
  }
  for (int k = 1; k <= n; k++)
    for (int i = 1; i <= n; i++)
      for (int j = 1; j <= n; j++)
        dis[i][j] = min(dis[i][j], dis[i][k] + dis[k][j]);
  double ans = 1e100;
  for (int j = 1; j <= m; j++) {
    v.clear();
    for (int i = 1; i <= n; i++)
      v.push_back(make_pair(dis[i][edge[j][0]], dis[i][edge[j][1]]));
    sort(v.begin(), v.end());
    int cnt = 0;
    for (int i = 0; i < n; i++) {
      while (cnt && xulie[cnt].second < v[i].second) cnt--;
      xulie[++cnt] = v[i];
    }
    int tmp = 1 << 30;
    for (int i = 2; i <= cnt; i++)
      tmp = min(tmp, xulie[i - 1].first + xulie[i].second);
    ans = min(ans, (1.0 * tmp + 1.0 * edge[j][2]) * 0.5);
  }
  printf("%.15lf\n", ans);
}
