n,S=map(int,input().split())
e=[[] for i in range(n)]
p=[0]+list(map(int,input().split()))
for i in range(1,n):
  e[p[i]-1]+=[i]
g=[(0,0)]+[tuple(map(int,input().split())) for i in range(1,n)]
X=10**15
u=[0]*n
v=[0]*n
h=[[] for i in range(n)]
q=[0]
while len(q)>0:
  s=q[-1]
  if v[s]==0:
    v[s]=1
    q+=e[s]
  else:
    u[s]=g[s][1]
    h[s]=[X]*(u[s]+1)
    h[s][g[s][1]]=g[s][0]
    for t in e[s]:
      nu=u[s]+u[t]
      nh=h[s]+[X]*u[t]
      for i in range(u[s]+1):
        for j in range(u[t]+1):
          nh[i+j]=min(nh[i+j],h[s][i]+h[t][j])
      h[s]=nh[:]
      u[s]=nu
    v[s]=0
    q.pop()
print(min(h[0][S:]))