#include <bits/stdc++.h> using namespace std; typedef long long ll; typedef pair<int, int> pii; #define fi first #define se second #define mp make_pair #define fastIO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0); const int N = 400; const int C = 2 * N * N; const int M = 2 * C; const ll inf = (ll)1e18; vector<pii> T[N]; ll dp[N][M]; void dfs(int u){ if(T[u].empty()){ for(int i = 0 ; i < M; i ++ ){ dp[u][i] = abs(i-C); } return; } for(int i = 0 ; i < M; i ++ ){ dp[u][i]=0; } for(auto x : T[u]){ dfs(x.fi); for(int j = 0; j < M; j ++ ){ if(j < x.se) dp[u][j] = inf; else dp[u][j] += dp[x.fi][j-x.se]; dp[u][j]=min(dp[u][j],inf); } } ll di = inf; for(int i = 0 ; i < M; i ++ ){ di ++ ; if(di < dp[u][i]){ dp[u][i] = di; } else{ di = dp[u][i]; } } di = inf; for(int i = M - 1; i >= 0 ; i -- ){ di ++ ; if(di < dp[u][i]){ dp[u][i] = di; } else{ di = dp[u][i]; } } } int main(){ fastIO; int n, m; cin >> n >> m; for(int i = 2; i <= n + m ; i ++ ){ int p, c; cin >> p >> c; T[p].push_back(mp(i, c)); } dfs(1); ll res = inf; for(int i = 0 ; i < M; i ++ ){ res = min(res, dp[1][i]); } cout << res << "\n"; return 0; }