#include <bits/stdc++.h>
using namespace std;
const int N = 210;
int n, m;
int f[N][N], rk[N][N];
int main() {
  memset(f, 60, sizeof(f));
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++) f[i][i] = 0;
  for (int i = 1; i <= m; i++) {
    int x, y, v;
    scanf("%d%d%d", &x, &y, &v);
    f[x][y] = f[y][x] = min(f[x][y], v);
  }
  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]);
      }
    }
  }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) rk[i][j] = j;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      for (int k = j + 1; k <= n; k++) {
        if (f[i][rk[i][j]] < f[i][rk[i][k]]) swap(rk[i][j], rk[i][k]);
      }
    }
  }
  int ans = f[0][0];
  for (int i = 1; i <= n; i++) {
    ans = min(ans, f[i][rk[i][1]] + f[i][rk[i][2]]);
    for (int j = i + 1; j <= n; j++) {
      for (int u = 1, v = 2; v <= n; v++) {
        if (f[j][rk[i][u]] < f[j][rk[i][v]]) {
          ans = min(ans, f[j][rk[i][u]] + f[i][rk[i][v]] + f[i][j]);
          u = v;
        }
      }
    }
  }
  printf("%lf", ans / 2.0);
  return 0;
}
