/*
_____
.' '.
/ 0 0 \
| ^ |
| \ / |
\ '---' /
'._____.'
*/
#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
struct chash
{
int operator()(int x) const
{
x ^= (x >> 20) ^ (x >> 12);
return x ^ (x >> 7) ^ (x >> 4);
}
};
template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename U> using hashtable = gp_hash_table<T, U, chash>;
random_device(rd);
mt19937 rng(rd());
template<class T>
void readi(T &x)
{
T input = 0;
bool negative = false;
char c = ' ';
while (c < '-')
{
c = getchar();
}
if (c == '-')
{
negative = true;
c = getchar();
}
while (c >= '0')
{
input = input * 10 + (c - '0');
c = getchar();
}
if (negative)
{
input = -input;
}
x = input;
}
template<class T>
void printi(T output)
{
if (output == 0)
{
putchar('0');
return;
}
if (output < 0)
{
putchar('-');
output = -output;
}
int aout[20];
int ilen = 0;
while(output)
{
aout[ilen] = ((output % 10));
output /= 10;
ilen++;
}
for (int i = ilen - 1; i >= 0; i--)
{
putchar(aout[i] + '0');
}
return;
}
template<class T>
void ckmin(T &a, T b)
{
a = min(a, b);
}
template<class T>
void ckmax(T &a, T b)
{
a = max(a, b);
}
template<class T, class U>
T nmod(T &x, U mod)
{
if (x >= mod) x -= mod;
}
template<class T>
T gcd(T a, T b)
{
return (b ? gcd(b, a % b) : a);
}
template<class T>
T randomize(T mod)
{
return (uniform_int_distribution<T>(0, mod - 1))(rng);
}
#define y0 ___y0
#define y1 ___y1
#define MP make_pair
#define MT make_tuple
#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
#define debug(x) cerr << #x << " = " << x << endl;
const long double PI = 4.0 * atan(1.0);
const long double EPS = 1e-10;
#define MAGIC 347
#define SINF 10007
#define CO 1000007
#define INF 1000000007
#define BIG 1000000931
#define LARGE 1696969696967ll
#define GIANT 2564008813937411ll
#define LLINF 2696969696969696969ll
#define MAXN 313
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;
int N, M;
int parent[MAXN];
ll dup[MAXN];
vector<int> edge[MAXN];
ll dp[MAXN][MAXN];
ll ans;
int32_t main()
{
ios_base::sync_with_stdio(0);
// cout << fixed << setprecision(10);
// cerr << fixed << setprecision(10);
// freopen ("file.in", "r", stdin);
// freopen ("file.out", "w", stdout);
cin >> N >> M;
M += N;
swap(N, M);
for (int i = 1; i < N; i++)
{
cin >> parent[i] >> dup[i];
parent[i]--;
edge[parent[i]].PB(i);
}
for (int i = 0; i < N; i++)
{
for (int j = 0; j < MAXN; j++)
{
dp[i][j] = LLINF;
}
if (i >= M) dp[i][0] = 0;
}
// cerr << M << " nons\n";
for (int u = M - 1; u >= 0; u--)
{
//u want to make all ur children the same
//so say currently they're a, b, c, d, e, f, etc
for (int i = 0; i < MAXN; i++)
{
dp[u][i] = 0;
for (int v : edge[u])
{
ll cost = LLINF;
for (int j = 0; j < MAXN; j++)
{
if (i >= j)
{
ckmin(cost, dp[v][j] + abs(i - (j + dup[v])));
}
}
dp[u][i] += cost;
ckmin(dp[u][i], LLINF);
}
// if (dp[u][i] == 1912)
// {
// cerr << "dp vertex " << u << " height " << i << " is " << dp[u][i] << endl;
// }
}
}
ans = LLINF;
for (int i = 0; i < MAXN; i++)
{
ckmin(ans, dp[0][i]);
}
cout << ans << '\n';
// cerr << "time elapsed = " << (clock() / (CLOCKS_PER_SEC / 1000)) << " ms" << endl;
return 0;
}
