from types import GeneratorType

def bootstrap(f, stack=[]):
    def wrappedfunc(*args, **kwargs):
        if stack:
            return f(*args, **kwargs)
        to = f(*args, **kwargs)
        while True:
            if type(to) is GeneratorType:
                stack.append(to)
                to = next(to)
            else:
                stack.pop()
                if not stack:
                    break
                to = stack[-1].send(to)
        return to
    return wrappedfunc

INF = 1<<60

N, X = map(int, input().split())
P = list(map(int, input().split()))
CS = [[0, 0]]+[list(map(int, input().split())) for _ in range(N-1)]
C, S = map(list, zip(*CS))

G = [[] for _ in range(N)]
for i, p in enumerate(P):
    G[p-1].append(i+1)

@bootstrap
def dfs(n, p):
    size[n] = S[n]
    dp[n] = [INF]*(size[n]+1)
    dp[n][-1] = C[n]
    for v in G[n]:
        if v == p:
            continue
        yield dfs(v, n)
        merge = [INF]*(size[n]+size[v]+1)
        for i in range(size[n]+1):
            for j in range(size[v]+1):
                merge[i+j] = min(merge[i+j], dp[n][i]+dp[v][j])
        size[n] += size[v]
        dp[n] = merge
    dp[n][0] = 0
    yield

dp = [[] for _ in range(N)]
size = [0]*N
dfs(0, -1)

print(min(dp[0][X:]))