INF = float('inf')
class Graph(object):
    def __init__(self, n=505):
        self.matrix = [[INF for _ in range(n)]for _ in range(n)]
        self.n = n

    def add(self,a,b,w):
        self.matrix[a][b] = min(self.matrix[a][b],w)

    def prim(self,n):
        cnt = 0
        p = [INF] * (n+1)
        st = [False] * (n+1)
        for _ in range(n):
            l = -1
            for idx, i in enumerate(p[1:]):
                if not st[idx+1] and (l == -1 or p[l] > p[idx+1]):
                    l = idx+1
            st[l] = True
            if l != 1 and p[l] == INF:
                return 'impossible'
            if l != 1:
                cnt += p[l]
            for i in range(1,n+1):
                if not st[i]:
                    p[i] = min(p[i], self.matrix[l][i])
        return cnt

n,m = map(int, input().split(' '))
g = Graph()
for _ in range(m):
    a,b,w = map(int,input().split(' '))
    g.add(a,b,w)
    g.add(b,a,w)
print(g.prim(n))