#include <bits/stdc++.h>
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
using namespace std;
typedef long long ll;
const int MAXN = (int)3e5 + 5;
struct dp_t {
ll h0, a0;
multiset<ll> S;
dp_t() {
h0 = a0 = 0;
}
ll get(ll x) {
ll val = h0;
ll slope = a0;
ll pos = 0;
for (ll pt : S) {
if (pt >= x) {
break;
}
val += slope * (pt - pos);
pos = pt;
slope++;
}
val += (x - pos) * slope;
return val;
}
} dp[MAXN];
int par[MAXN], edge_len[MAXN];
vector<int> adj[MAXN];
int n, m;
int main() {
cin >> n >> m;
for (int i = 2; i <= n + m; i++) {
cin >> par[i] >> edge_len[i];
adj[par[i]].push_back(i);
}
for (int v = n + m; v > n; v--) {
dp[v].h0 = edge_len[v];
dp[v].a0 = -1;
dp[v].S.insert(edge_len[v]);
dp[v].S.insert(edge_len[v]);
}
for (int v = n; v > 0; v--) {
for (int to : adj[v]) {
dp[v].h0 += dp[to].h0;
dp[v].a0 += dp[to].a0;
if (sz(dp[to].S) > sz(dp[v].S)) {
dp[v].S.swap(dp[to].S);
}
for (ll pt : dp[to].S) {
dp[v].S.insert(pt);
}
dp[to].S.clear();
}
while (!dp[v].S.empty() && dp[v].a0 + sz(dp[v].S) > 1) {
dp[v].S.erase(prev(dp[v].S.end()));
}
assert(sz(dp[v].S) >= 2);
dp[v].h0 += edge_len[v];
ll P = *dp[v].S.rbegin();
dp[v].S.erase(prev(dp[v].S.end()));
ll Q = *dp[v].S.rbegin();
dp[v].S.erase(prev(dp[v].S.end()));
dp[v].S.insert(P + edge_len[v]);
dp[v].S.insert(Q + edge_len[v]);
}
ll val = dp[1].h0, slope = dp[1].a0;
ll pos = 0;
for (ll pt : dp[1].S) {
val += (pt - pos) * slope;
pos = pt;
slope++;
if (slope == 0) break;
}
cout << val << endl;
return 0;
}
