#include "bits/stdc++.h"
using namespace std;
#define ar array
#define int long long
const int N = 305;
const int inf = 1e18;
vector<ar<int, 2>> edges[N];
int dp[N][N];
void dfs(int u){
for(auto x : edges[u]){
dfs(x[0]);
for(int j=0;j<N;j++){
int pre = dp[u][j]; dp[u][j] = inf;
for(int l=0;l<=j;l++){
dp[u][j] = min(dp[u][j], pre + dp[x[0]][l] + abs(j - l - x[1]));
}
}
}
if(edges[u].empty()){
memset(dp[u], 63, sizeof dp[u]);
dp[u][0] = 0;
}
}
signed main(){
ios::sync_with_stdio(0); cin.tie(0);
int n, m; cin>>n>>m;
for(int i=1;i<n+m;i++){
int p, c; cin>>p>>c;
edges[--p].push_back({i, c});
}
if(n == 1){
sort(edges[0].begin(), edges[0].end(), [&](auto& a, auto& b){
return a[1] < b[1];
});
int C = edges[0][m / 2][1];
long long res = 0;
for(auto x : edges[0]) res += abs(C - x[1]);
cout<<res<<"\n";
return 0;
}
dfs(0);
int i = 1;
while(i < N && dp[0][i] <= dp[0][i-1]) i++;
cout<<dp[0][i-1]<<"\n";
while(i < N && dp[0][i] > dp[0][i-1]) i++;
assert(i == N);
}
