N = gets.to_i
dist = Array.new(N) {Array.new(N, Float::INFINITY)}

(N-1).times {
	u, v, d = gets.split(" ").map{|s| s.to_i}
	dist[u-1][v-1] = dist[v-1][u-1] = d
}

0.upto(N-1) {|k|
	dist[k][k] = 0
	0.upto(N-1) {|i|
		0.upto(N-1) {|j|
			dist[i][j] = [dist[i][j], dist[i][k] + dist[k][j]].min
		}
	}
}

cnt = 0
0.upto(N-1) {|i|
	0.upto(N-1) {|j|
		cnt += dist[i][j]
	}
}

puts cnt