n, x = map(int, input().split())
P = [0] + list(map(int, input().split()))
P = [P[i]-1 for i in range(n)]
V = [[] for _ in range(n)]
for i in range(1, n):
    V[P[i]].append(i)
CS = [(0, 0)] + [tuple(map(int, input().split())) for _ in range(n-1)]
from collections import deque
dq = deque([0])
D = [-1] * n; D[0] = 0
DD = [[] for _ in range(n+1)]
while dq:
    now = dq.popleft()
    DD[D[now]].append(now)
    for nxt in V[now]:
        D[nxt] = D[now] + 1
        dq.append(nxt)
dp = [[0] for _ in range(n)]

inf = 1 << 50
def merge(A0, A1):
    a0 = len(A0)-1
    a1 = len(A1)-1
    ndp = [inf] * (a0 + a1 + 1)
    for now in range(a0+1):
        for nxt in range(a1+1):
            ndp[now+nxt] = min(ndp[now+nxt], A0[now]+A1[nxt])
    return ndp

for d in range(n, -1, -1):
    for now in DD[d]:
        for nxt in V[now]:
            dp[now] = merge(dp[now], dp[nxt])[:]
        c, s = CS[now]
        ndp = [inf] * (s + len(dp[now]))
        ndp[0] = 0
        for i in range(len(dp[now])):
            ndp[i+s] = dp[now][i]+c
        dp[now] = ndp[:]

ans = inf
for i in range(x, len(dp[0])):
    ans = min(ans, dp[0][i])
print(ans)