#include <bits/stdc++.h>
using namespace std;
#define int long long
int inf = 1e18;
int n, m;
int t[300005], c[300005];
vector<int> f[300005];
int h[300005];
int dp[305][305];
void root(int nod)
{
for (auto fiu : f[nod])
{
h[fiu] = c[fiu] + h[nod];
root(fiu);
}
}
void calc(int nod)
{
for (auto fiu : f[nod])
calc(fiu);
if (f[nod].empty())
{
for (int i = 0; i <= 300; i++)
dp[nod][i] = abs(i - c[nod]);
}
else
{
/*for (int i = 0; i <= 300; i++)
{
dp[nod][i] = inf;
for (int j = 0; j <= i; j++)
{
int ct = abs(j - c[nod]);
for (auto fiu : f[nod])
ct += dp[fiu][i - j];
dp[nod][i] = min(dp[nod][i], ct);
}
}*/
for (int i = 0; i <= 300; i++)
dp[nod][i] = inf;
for (int i = c[nod]; i <= 300; i++)
{
int ct = 0;
for (auto fiu : f[nod])
ct += dp[fiu][i - c[nod]];
dp[nod][i] = ct;
}
for (int itr = 1; itr <= 300; itr++)
{
for (int i = 300; i >= 1; i--)
dp[nod][i] = min(dp[nod][i], dp[nod][i - 1] + 1);
}
for (int itr = 1; itr <= c[nod]; itr++)
{
for (int i = 0; i < 300; i++)
dp[nod][i] = min(dp[nod][i], dp[nod][i + 1] + 1);
}
}
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
cin >> n >> m;
n += m;
for (int i = 2; i <= n; i++)
{
cin >> t[i] >> c[i];
f[t[i]].push_back(i);
}
root(1);
calc(1);
int mnm = inf;
for (auto i = 0; i <= 300; i++)
mnm = min(mnm, dp[1][i]);
cout << mnm;
return 0;
}
