#include <bits/stdc++.h>
using namespace std;
int a[40005], b[40005], c[40005], f[205][205];
int n, m;
vector<pair<int, int> > v;
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      if (i != j) f[i][j] = 1000000007;
    }
  }
  for (int i = 1; i <= m; i++) {
    scanf("%d%d%d", &a[i], &b[i], &c[i]);
    c[i] <<= 1;
    f[a[i]][b[i]] = f[b[i]][a[i]] = min(f[b[i]][a[i]], c[i]);
  }
  for (int k = 1; k <= n; k++) {
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j <= n; j++) {
        f[i][j] = min(f[i][j], f[i][k] + f[k][j]);
      }
    }
  }
  int ans = 2147483647;
  for (int i = 1; i <= m; i++) {
    int x = a[i], y = b[i], r = 0;
    v.clear();
    for (int j = 1; j <= n; j++) {
      v.push_back(make_pair(f[x][j], j));
    }
    sort(v.begin(), v.end());
    for (int j = (int)v.size() - 1; j >= 0; j--) {
      int l = v[j].first, mid = (l + r + c[i]) / 2;
      if (mid >= l && mid <= l + c[i]) ans = min(ans, mid);
      r = max(r, f[y][v[j].second]);
    }
  }
  printf("%.1lf\n", 1.0 * ans / 2);
  return 0;
}
