def main():
    import sys
    input_data = sys.stdin.read().strip().split()
    if not input_data:
        return
    it = iter(input_data)
    N = int(next(it))
    M = int(next(it))
    
    # 道路候補のリスト．各候補は (重み, u, v) として格納する．
    # ここで重み = 6/(7-C) となる．
    edges = []
    for _ in range(M):
        u = int(next(it))
        v = int(next(it))
        c = int(next(it))
        weight = 6 / (7 - c)
        # インデックスは 0-indexed にする
        edges.append((weight, u - 1, v - 1))
    
    # Kruskal法のため重みでソート
    edges.sort(key=lambda x: x[0])
    
    parent = list(range(N))
    def find(x):
        if parent[x] != x:
            parent[x] = find(parent[x])
        return parent[x]
    
    total_expectation = 0.0
    count = 0
    for w, u, v in edges:
        ru, rv = find(u), find(v)
        if ru != rv:
            parent[ru] = rv
            total_expectation += w
            count += 1
            if count == N - 1:
                break
    
    print(total_expectation)

if __name__ == '__main__':
    main()