# input
import sys
input = sys.stdin.readline
II = lambda : int(input())
MI = lambda : map(int, input().split())
LI = lambda : [int(a) for a in input().split()]
SI = lambda : input().rstrip()
LLI = lambda n : [[int(a) for a in input().split()] for _ in range(n)]
LSI = lambda n : [input().rstrip() for _ in range(n)]
MI_1 = lambda : map(lambda x:int(x)-1, input().split())
LI_1 = lambda : [int(a)-1 for a in input().split()]

mod = 998244353
inf = 1001001001001001001
ordalp = lambda s : ord(s)-65 if s.isupper() else ord(s)-97
ordallalp = lambda s : ord(s)-39 if s.isupper() else ord(s)-97
yes = lambda : print("Yes")
no = lambda : print("No")
yn = lambda flag : print("Yes" if flag else "No")

prinf = lambda ans : print(ans if ans < 1000001001001001001 else -1)
alplow = "abcdefghijklmnopqrstuvwxyz"
alpup = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
alpall = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
URDL = {'U':(-1,0), 'R':(0,1), 'D':(1,0), 'L':(0,-1)}
DIR_4 = [[-1,0],[0,1],[1,0],[0,-1]]
DIR_8 = [[-1,0],[-1,1],[0,1],[1,1],[1,0],[1,-1],[0,-1],[-1,-1]]
DIR_BISHOP = [[-1,1],[1,1],[1,-1],[-1,-1]]
prime60 = [2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59]
sys.set_int_max_str_digits(0)
# sys.setrecursionlimit(10**6)
# import pypyjit
# pypyjit.set_param('max_unroll_recursion=-1')

from collections import defaultdict,deque
from heapq import heappop,heappush
from bisect import bisect_left,bisect_right
DD = defaultdict
BSL = bisect_left
BSR = bisect_right

n, x = MI()
par = [-1] + LI_1()

dp = [[inf] for i in range(n)] # 開放する
for i in range(1, n):
    c, s = MI()
    dp[i] = [inf] * (s + 1)
    dp[i][s] = c

c = [0] * n
for i in par[1:n]:
    c[i] += 1

st = [u for u in range(n) if c[u] == 0]

dp[0][0] = 0

while st:
    u = st.pop()
    if u == 0:
        print(min(dp[0][x:]))
        # print(dp)
        exit()
    
    # 自分を開放する時
    p = par[u]
    dp[u][0] = 0
    lu = len(dp[u])
    lp = len(dp[p])
    ndp = [inf] * (lu + lp - 1)
    for i in range(lu):
        for j in range(lp):
            ndp[i+j] = min(ndp[i+j], dp[u][i] + dp[p][j])
    
    dp[p] = ndp
    
    c[p] -= 1
    if c[p] == 0: st.append(p)