def merge(x,y):
    ret=[1<<60]*(len(x)+len(y)-1)
    for i in range(len(x)):
        for j in range(len(y)):
            ret[i+j]=min(ret[i+j],x[i]+y[j])
    return ret

N,X=map(int,input().split())
p=list(map(int,input().split()))
res=[(0,0)]+[tuple(map(int,input().split())) for i in range(N-1)]
tree=[[] for i in range(N)]
for i in range(N-1):
    tree[p[i]-1].append(i+1)
dp=[[0] for i in range(N)]
for i in reversed(range(N)):
    for j in tree[i]:
        dp[i]=merge(dp[i],dp[j])
    ndp=[1<<60]*(res[i][1]+len(dp[i]))
    ndp[0]=0
    for j in reversed(range(len(dp[i]))):
        ndp[j+res[i][1]]=min(ndp[j+res[i][1]],dp[i][j]+res[i][0])
    dp[i]=ndp
ans=1<<60
for i in range(X,len(dp[0])):
    ans=min(ans,dp[0][i])
print(ans)