#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define all(a) a.begin(),a.end()
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef unsigned long long ull;
typedef vector<int> vi;
const int mxn = 600+1;
vector<pii> g[mxn];
ll dp[mxn][400];
void dfs(int u = 1, int col = 0){
for(auto [v,c] : g[u]){
dfs(v,c);
for(int i = 0; i < 400; i++)
dp[u][i] += dp[v][i];
}
if(g[u].empty()){
for(int i = 0; i <= 399; i++)
dp[u][i] = abs(i-col);
}else{
for(int i = 399; i >= 0; i--)
for(int j = i; j >= 0; j--)
dp[u][i] = min(dp[u][i],dp[u][j] + abs((i-j)-col));
}
}
void solve(){
int n,m; cin >> n >> m;
for(int i = 2; i <= n+m; i++){
int p,c; cin >> p >> c;
g[p].emplace_back(pii{i,c});
}
dfs();
cout << *min_element(dp[1],dp[1]+400);
}
signed main(){
cin.tie(0)->sync_with_stdio(0);
int t = 1;
// cin >> t;
while(t--){solve();}
}
