import pypyjit
pypyjit.set_param("max_unroll_recursion=-1")
import sys
sys.setrecursionlimit(10**4)
N,X = list(map(int,input().split()))
P = [-1] + list(map(lambda x:int(x)-1,input().split()))
edge = [[] for _ in range(N)]
for i in range(1,N):
    edge[i].append(P[i])
    edge[P[i]].append(i)

points = [(0,0)]
for _ in range(1,N):
    c,s = list(map(int,input().split()))
    points.append((c,s))

INF = 1<<60
def dfs(n,pre):
    ret = [INF] * (X+1)
    ret[X] = 0
    c,s = points[n]
    ret[max(0, X-s)] = 0
    for i in edge[n]:
        if(i == pre):continue
        child = dfs(i, n)
        for j in range(X+1):
            if(ret[j] == INF):continue
            for k in range(X+1):
                ret[max(0,j-(X-k))] = min(ret[max(0,j-(X-k))], ret[j] + child[k] + points[i][0])

    return ret

print(dfs(0,-1)[0])