N,X=map(int,input().split())
P=list(map(int,input().split()))
edge = [[] for _ in range(N)]
d = [[0,0]]
for i in range(N-1):
    c,s=map(int,input().split())
    d.append((c,s))
    edge[P[i]-1].append(i+1)
inf = 10**30
dp = [[0] for _ in range(N)]

def merge(a,b):
    res = [inf]*(len(a) + len(b) - 1)
    for i in range(len(a)):
        for j in range(len(b)):
            res[i+j] = min(res[i+j],a[i]+b[j])
    return res

for i in range(N-1,-1,-1):
    for e in edge[i]:
        dp[i] = merge(dp[i], dp[e])
    c,s = d[i]
    if s>0:
        dp[i] = [0]+[inf]*(s-1)+[c + d for d in dp[i]]
    else:
        dp[i][0] = 0
print(min(dp[0][X:]))