#include <bits/stdc++.h>
using namespace std;
using ll = long long;
struct slope_trick{
long long mn;
priority_queue<long long> L;
priority_queue<long long, vector<long long>, greater<long long>> R;
ll ofs = 0;
slope_trick(){
mn = 0;
}
long long get_min(){
return mn;
}
void add_right(long long a){
if (!L.empty()){
mn += max(L.top() - a, (long long) 0);
}
L.push(a);
R.push(L.top()-ofs);
L.pop();
}
void add_left(long long a){
if (!R.empty()){
mn += max(a - (R.top()+ofs), (long long) 0);
}
R.push(a-ofs);
L.push(R.top()+ofs);
R.pop();
}
void conv(long long a){
long long x = L.top();
L.pop();
L.push(x + a);
ofs+=a;
}
slope_trick& operator +=(slope_trick f){
mn += f.mn;
while (!f.R.empty()){
add_right(f.R.top());
f.R.pop();
}
while (!f.L.empty()){
add_left(f.L.top());
f.L.pop();
}
return *this;
}
int size(){
return L.size() + R.size();
}
};
int main(){
int N, M;
cin >> N >> M;
vector<int> P(N + M), C(N + M);
for (int i = 1; i < N + M; i++){
cin >> P[i] >> C[i];
P[i]--;
}
vector<vector<int>> c(N + M);
for (int i = 1; i < N + M; i++){
c[P[i]].push_back(i);
}
vector<slope_trick> dp(N + M);
for (int i = N; i < N + M; i++){
dp[i].add_left(0);
dp[i].add_right(0);
}
for (int i = N - 1; i >= 0; i--){
for (int j : c[i]){
dp[j].conv(C[j]);
}
for (int j : c[i]){
if (dp[j].size() > dp[i].size()){
swap(dp[i], dp[j]);
}
dp[i] += dp[j];
}
}
cout << dp[0].get_min() << endl;
}
