
Score : 600 points
Problem StatementThe server in company A has a structure where N devices numbered 1, 2, ..., N are connected with N - 1 cables.
The i-th cable connects Device U_i and Device V_i.
Any two different devices are connected through some number of cables.
Each device v (1 \leq v \leq N) has a non-zero integer A_v, which represents the following:
If A_v < 0, Device v is a computer that consumes an electric power of -A_v.
If A_v > 0, Device v is a battery that supplies an electric power of A_v.
You have decided to disconnect some number of cables (possibly zero) to disable the server.
When some cables are disconnected, the devices will be divided into some number of connected components.
The server will be disabled if all of these connected components satisfy one of the following conditions:
There is no computer in the connected component. That is, A_v is positive for every device v that belongs to the connected component.
There is not enough supply of electric power in the connected component. That is, the sum of A_v over all devices v that belong to the connected component is negative.
At least how many cables do you need to disconnect in order to disable the server?
Constraints
1 \leq N \leq 5 000
1 \leq |A_i| \leq 10^9 (1 \leq i \leq N)
1 \leq U_i, V_i \leq N (1 \leq i \leq N - 1)
U_i \neq V_i (1 \leq i \leq N - 1)
Any two different devices are connected through some number of cables.
All values in input are integers.
InputInput is given from Standard Input in the following format:
N
A_1 A_2 ... A_N
U_1 V_1
U_2 V_2
:
U_{N - 1} V_{N - 1}
OutputPrint the answer.
Sample Input 17
-2 7 5 6 -8 3 4
1 2
2 3
2 4
1 5
5 6
5 7
Sample Output 11
We should disconnect the cable connecting Device 1 and Device 2.
Sample Input 24
1 2 3 4
1 2
1 3
1 4
Sample Output 20
Sample Input 36
10 -1 10 -1 10 -1
1 2
2 3
3 4
4 5
5 6
Sample Output 35
Sample Input 48
-2 3 6 -2 -2 -5 3 2
3 4
7 6
6 2
8 2
5 3
1 8
3 7
Sample Output 43
Sample Input 510
3 4 9 6 1 5 -1 10 -10 -10
7 4
5 6
8 1
9 5
7 1
10 3
2 8
4 10
9 2
Sample Output 53
