#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int Nmax = 6e5 + 5;
vector<int> v[Nmax];
ll opt[Nmax], A[Nmax], B[Nmax];
int up[Nmax];
int n, m;
ll moove(ll x, ll l, ll r)
{
if(x < l) return l - x;
if(x > r) return x - r;
return 0;
}
void dfs(int node)
{
if(v[node].empty())
{
opt[node] = 0;
A[node] = up[node];
B[node] = up[node];
return;
}
for(auto son : v[node]) dfs(son);
map<ll,int> change;
for(auto son : v[node])
{
change[0] -= 1;
change[A[son]] += 1;
change[B[son]] += 1;
}
int sum = 0;
ll L = -1, R = -1;
for(auto &it : change)
{
sum += it.second;
it.second = sum;
if(it.second >= 0 && L == -1) L = it.first;
if(it.second > 0 && R == -1) R = it.first;
}
A[node] = L;
B[node] = R;
ll s2 = 0;
for(auto son : v[node])
{
opt[node] += opt[son] + moove(L, A[son], B[son]);
s2 += opt[son] + moove(R, A[son], B[son]);
}
assert(opt[node] == s2);
A[node] += up[node];
B[node] += up[node];
}
int main()
{
// freopen("input", "r", stdin);
cin.sync_with_stdio(false); cin.tie(0);
int i, x;
cin >> n >> m; n += m;
for(i=2; i<=n; ++i)
{
cin >> x >> up[i];
v[x].push_back(i);
}
dfs(1);
cout << opt[1] << '\n';
return 0;
}
