#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define ALL(v) (v).begin(), (v).end()
#define MASK(i) (1LL << (i))
#define GETBIT(mask, i) (((mask) >> (i)) & 1)
// mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rng(1);
ll rngesus(ll l, ll r){return ((ull) rng()) % (r - l + 1) + l;}
ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll LASTBIT(ll mask){return mask & (-mask);}
ll pop_cnt(ll mask){return __builtin_popcountll(mask);}
ll ctz(ll mask){return __builtin_ctzll(mask);}
ll clz(ll mask){return __builtin_clzll(mask);}
ll logOf(ll mask){return 63 - clz(mask);}
template <class T1, class T2>
bool minimize(T1 &a, T2 b){
if (a > b){a = b; return true;}
return false;
}
template <class T1, class T2>
bool maximize(T1 &a, T2 b){
if (a < b){a = b; return true;}
return false;
}
template <class T>
void printArr(T& a, string separator = " ", string finish = "\n", ostream& out = cout){
for(auto i: a) out << i << separator;
out << finish;
}
template <class T>
void remove_dup(vector<T> &a){
sort(ALL(a));
a.resize(unique(ALL(a)) - a.begin());
}
const int N = 310;
const ll INF = 1e18 + 69;
int n, m;
vector<pair<int,int>> graph[N];
ll dp[N][N];
void dfs(int u){
if (u > n){
for(int i = 1; i<N; ++i) dp[u][i] = INF;
return;
}
for(pair<int, int> v: graph[u]){
dfs(v.first);
ll f[N];
for(int i = 0; i<N; ++i){
f[i] = INF;
for(int j = 0; j<=i; ++j){
minimize(f[i], dp[v.first][j] + abs(v.second - (i - j)));
}
}
for(int i = 0; i<N; ++i) dp[u][i] += f[i];
}
}
int main(void){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> m;
for(int i = 2; i<=n+m; ++i){
int p, c; cin >> p >> c;
graph[p].push_back({i, c});
}
dfs(1);
ll ans = INF;
for(int i = 0; i<N; ++i) minimize(ans, dp[1][i]);
cout << ans << "\n";
return 0;
}
