#include <cstdio>
#include <iostream>
#include <algorithm>
#include <string>
#include <cstring>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <cmath>
#include <iomanip>
#include <cassert>
#include <bitset>
#include <random>
#include <ctime>
using namespace std;
typedef pair<int, int> P;
#define rep(i, n) for (int i=0; i<(n); i++)
#define all(c) (c).begin(), (c).end()
#define uniq(c) c.erase(unique(all(c)), (c).end())
#define index(xs, x) (int)(lower_bound(all(xs), x) - xs.begin())
#define _1 first
#define _2 second
#define pb push_back
#define INF (1LL<<50)
#define MOD 1000000007
long long diff = 0;
struct DS {
multiset<long long> left, right;
void balance() {
if ((left.size()+right.size())%2 == 0) {
while (left.size() > right.size()) {
auto it = --left.end();
right.insert(*it);
left.erase(it);
}
while (left.size() < right.size()) {
auto it = right.begin();
left.insert(*it);
right.erase(it);
}
}
}
void add(long long x) {
if (!right.empty() && x <= *right.begin()) left.insert(x);
else right.insert(x);
balance();
}
void extend(long long p) {
if (left.empty()) return;
auto it = --left.end();
long long last = *it;
left.erase(it);
//cout<<"diff-="<<p<<"\n";
//diff -= p;
left.insert(last+p);
long long lp = *right.begin();
right.erase(right.begin());
while (!right.empty() && *right.begin() < INF) {
auto it = right.begin();
long long cur = *it;
//cout<<"diff-=INF\n";
diff -= INF;
right.erase(it);
right.insert(cur+INF);
}
right.insert(lp+p);
assert(left.size() == right.size());
//balance();
}
int size() {
assert(left.size() == right.size());
return left.size();
}
vector<long long> enumerate() {
vector<long long> ret;
for (long long x : left) ret.pb(x);
for (long long x : right) ret.pb(x);
return ret;
}
};
int N, M;
int U[300000], C[300000];
DS dp[300000];
signed main() {
ios::sync_with_stdio(false); cin.tie(0);
cin >> N >> M;
for (int i=1; i<N+M; i++) {
cin >> U[i] >> C[i];
U[i]--;
}
for (int i=N+M-1; i>0; i--) {
if (i >= N) dp[i].add(0), dp[i].add(0);
dp[i].extend(C[i]);
//cout<<"dp["<<i<<"] = {"; for (long long x : dp[i].enumerate()) cout<<x<<",";cout<<"}\n";
if (dp[U[i]].size() < dp[i].size()) swap(dp[U[i]], dp[i]);
vector<long long> vs = dp[i].enumerate();
for (long long x : vs) dp[U[i]].add(x);
}
long long sum = 0;
//cout<<"dp["<<0<<"] = {"; for (long long x : dp[0].enumerate()) cout<<x<<",";cout<<"}\n";
long long X = *dp[0].left.rbegin();
//cout<<"X="<<X<<"\n";
vector<long long> vs = dp[0].enumerate();
for (long long x : vs) sum += abs(X-x);
//cout<<"sum="<<sum<<", diff="<<diff<<"\n";
sum += diff;
sum /= 2;
cout << sum << "\n";
return 0;
}
