'''
Prim 最小生成树算法
'''


# 普利姆算法求解最小生成树输入为边列表，每条边表示为(起点，终点，权重)
# 返回最小生成树权重总和，以及最小生成树边列表, 生成不了最小生成树返回None

from queue import PriorityQueue
def getMinSpanTreePrim(edges):
    if len(edges) == 0:
        return [0, []]

    span_tree = []
    node_set = set()
    link = {}
    for a, b, w in edges:
        node_set.add(a)
        node_set.add(b)

        if a not in link:
            link[a] = []
        if b not in link:
            link[b] = []

        link[a].append((b, w))
        link[b].append((a, w))

    node = None
    sum = 0

    min_heap = PriorityQueue()
    visited = set()
    for _ in range(len(node_set)):
        if node is None:
            node = edges[0][0]
            visited.add(node)
            for next, w in link[node]:
                min_heap.put((w, node, next))
        else:
            while True:
                if min_heap.empty():
                    return [None, None]

                w, node1, node2 = min_heap.get()
                if not (node1 in visited and node2 in visited):
                    sum += w
                    span_tree.append((node1, node2))

                    for node in [node1, node2]:
                        if node not in visited:
                            visited.add(node)
                            for next, w in link[node]:
                                min_heap.put((w, node, next))

                    break

    return [sum, span_tree] if len(span_tree) == len(node_set) - 1 else [None, None]


n, m = map(int, input().split())
edges = []
for _ in range(m):
    a, b, w = map(int, input().split())
    edges.append((a, b, w))
ans = getMinSpanTreePrim(edges)
print(ans[0] if ans[0] is not None else 'impossible')