#include <bits/stdc++.h>
#define endl '\n'
//#pragma GCC optimize("Ofast")
using namespace std;
using ll = long long;
using ld = long double;
using pii = pair < int, int >;
using pll = pair < ll, ll >;
const ll INF = 2e18;
const ll DIM = 300007;
const ld PI = 3.1415926535;
const int mod = 999999893;
class convexFunction {
public:
convexFunction() {
k = 0;
b = 0;
}
ll getL() {
return x[max((int)x.size() - (int)k - 1, 0)];
}
ll getR() {
if(k == 0) return INF;
return x[max((int)x.size() - (int)k - 1, 0) + 1];
}
ll getMi() {
ll res = b;
int ind = max((int)x.size() - (int)k - 1, 0);
for(int i = x.size() - 1; i > ind; i--) {
res += x[i];
}
ll resk = k - (x.size() - 1 - ind);
return resk * x[max((int)x.size() - (int)k - 1, 0)] + res;
}
vector < ll > x;
ll k, b;
};
vector < ll > merge(vector < ll >& v1, vector < ll >& v2) {
vector < ll > res;
int p1 = 0, p2 = 0;
while(p1 < v1.size() || p2 < v2.size()) {
if(p1 == v1.size()) res.push_back(v2[p2++]);
else if(p2 == v2.size()) res.push_back(v1[p1++]);
else {
if(v1[p1] <= v2[p2]) res.push_back(v1[p1++]);
else res.push_back(v2[p2++]);
}
}
return res;
}
void merge(convexFunction& f1, convexFunction& f2) {
if(f1.x.size() < f2.x.size()) swap(f1, f2);
f1.k += f2.k;
f1.b += f2.b;
f1.x = merge(f1.x, f2.x);
f2.x.clear();
}
int n, m;
vector < int > v[DIM];
ll p[DIM], c[DIM];
convexFunction f[DIM];
void dfs(int val) {
if(v[val].size() == 0) {
f[val].x = {c[val], c[val]};
f[val].k = 1;
f[val].b = -c[val];
return;
}
convexFunction g;
for(auto to: v[val]) {
dfs(to);
merge(g, f[to]);
}
if(val == 1) {
f[val] = g;
return;
}
ll L = g.getL(), R = g.getR();
for(int i = 0; i < g.x.size() && g.x[i] <= L; i++) {
f[val].x.push_back(g.x[i]);
}
f[val].x.pop_back();
f[val].x.push_back(L + c[val]);
f[val].x.push_back(R + c[val]);
f[val].k = 1;
f[val].b = g.getMi() - f[val].x.back();
//cout << val << " " << f[val].getMi() << endl;
}
int main() {
cin.tie(0); cout.tie(0); ios_base::sync_with_stdio(0);
#ifdef IloveCP
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
cin >> n >> m;
for(int i = 2; i <= n + m; i++) {
cin >> p[i] >> c[i];
v[p[i]].push_back(i);
}
dfs(1);
cout << f[1].getMi() << endl;
return 0;
}
