N, M = map(int, input().split())
D = [0] * N
for _ in range(M):
	u, v, w = map(int, input().split()); u -= 1; v -= 1
	D[u] += w; D[v] += w
D.sort(reverse = True)
print(sum((1 if i % 2 == 0 else -1) * D[i] for i in range(N)) // 2)