#include <stdio.h>
#include <string.h>
#define N 5000
#define INF 0x3f3f3f3f3f3f3f3fLL
long long min(long long a, long long b) { return a < b ? a : b; }
int merge(int *dd1, long long *ll1, int k1, int *dd2, long long *ll2, int k2) {
static int dd[N];
static long long ll[N];
int k, h1, h2;
k = 0, h1 = h2 = 0;
while (h1 < k1 && h2 < k2) {
long long l = min(ll1[h1], ll2[h2]);
dd[k] = dd1[h1] + dd2[h2], ll[k] = l, k++;
if ((ll1[h1] -= l) == 0)
h1++;
if ((ll2[h2] -= l) == 0)
h2++;
}
memcpy(dd1, dd, k * sizeof *dd);
memcpy(ll1, ll, k * sizeof *ll);
return k;
}
int main() {
static int pp[N], cc[N], dd[N][N], kk[N];
static long long dp[N], ll[N][N];
int n, m, n_, h, i;
long long ans;
scanf("%d%d", &n, &m), n_ = n + m;
for (i = 1; i < n_; i++)
scanf("%d%d", &pp[i], &cc[i]), pp[i]--;
for (i = n_ - 1; i > 0; i--) {
int p;
dp[i] += cc[i];
for (h = kk[i]; h > 0 && dd[i][h - 1] >= -1; h--)
dd[i][h] = dd[i][h - 1], ll[i][h] = ll[i][h - 1];
dd[i][h] = -1, ll[i][h] = cc[i], kk[i]++;
while (kk[i] && dd[i][kk[i] - 1] >= 1)
kk[i]--;
dd[i][kk[i]] = 1, ll[i][kk[i]] = INF, kk[i]++;
p = pp[i];
dp[p] += dp[i];
if (kk[p] == 0)
memcpy(dd[p], dd[i], kk[i] * sizeof *dd[i]), memcpy(ll[p], ll[i], kk[i] * sizeof *ll[i]), kk[p] = kk[i];
else
kk[p] = merge(dd[p], ll[p], kk[p], dd[i], ll[i], kk[i]);
}
ans = dp[0];
for (h = 0; h < kk[0] && dd[i][h] < 0; h++)
ans += dd[i][h] * ll[i][h];
printf("%lld\n", ans);
return 0;
}
