def test_size(self) -> None:
dsu = DSU(5)
dsu.merge(0, 1)
assert dsu.size(0) == 2
dsu.merge(0, 2)
assert dsu.size(0) == 3
# Test assertion of invalid indices
for i in (-1, 5):
with pytest.raises(AssertionError):
dsu.size(i)
def test_initial_status(self) -> None:
dsu = DSU(5)
for i, j in combinations(range(5), 2):
assert not dsu.same(i, j)
for index in range(5):
assert dsu.size(index) == 1
assert dsu.leader(index) == index
assert dsu.groups() == [[0], [1], [2], [3], [4]]
from atcoder.dsu import DSU
N = int(input())
edges = []
for _ in range(N - 1):
u, v, w = (int(x) for x in input().split())
edges.append((w, u - 1, v - 1))
edges.sort()
dsu = DSU(N)
ans = 0
for w, u, v in edges:
ans += w * dsu.size(u) * dsu.size(v)
dsu.merge(u, v)
print(ans)
