#include<bits/stdc++.h>
using namespace std;
#define int long long
#define nl '\n'
const int N = 301;
vector<pair<int,int>> g[N];
int dp[N][N];
void dfs(int v){
for(auto [ch, w] : g[v]){
dfs(ch);
for(int i=0; i<=300; i++){
int mn = 1e18;
for(int j=0; j<=i; j++){
int reqw = i - j;
mn = min(mn, dp[ch][j] + abs(w - reqw));
}
if(mn == 1e18){
dp[v][i] = 1e18;
break;
}
dp[v][i] += mn;
}
}
if(g[v].size() == 0){
for(int i=1; i<=300; i++) dp[v][i] = 1e18;
dp[v][0] = 0;
}
}
inline void solve(){
int n, m;
cin>>n>>m;
for(int i=2; i<=n+m; i++){
int p, c;
cin>>p>>c;
g[p].push_back({i, c});
}
dfs(1);
int ans = 1e18;
for(int i=0; i<=300; i++) ans = min(ans, dp[1][i]);
cout<<ans;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);cout.tie(NULL);
int t = 1;
//cin>>t;
while(t--) solve();
return 0;
}
