#include <algorithm>

#include  <iterator>

#include  <iostream>

#include   <cstring>

#include   <cstdlib>

#include   <iomanip>

#include    <bitset>

#include    <cctype>

#include    <cstdio>

#include    <string>

#include    <vector>

#include     <stack>

#include     <cmath>

#include     <queue>

#include      <list>

#include       <map>

#include       <set>

#include   <cassert>

using namespace std;

#define lson (l , mid , rt << 1)

#define rson (mid + 1 , r , rt << 1 | 1)

#define debug(x) cerr << #x << " = " << x << "\n";

#define pb push_back

#define pq priority_queue

typedef long long ll;

typedef unsigned long long ull;

//typedef __int128 bll;

typedef pair<ll ,ll > pll;

typedef pair<int ,int > pii;

typedef pair<int,pii> p3;

//priority_queue<int> q;//这是一个大根堆q

//priority_queue<int,vector<int>,greater<int> >q;//这是一个小根堆q

#define fi first

#define se second

//#define endl '\n'

#define OKC ios::sync_with_stdio(false);cin.tie(0)

#define FT(A,B,C) for(int A=B;A <= C;++A)  //用来压行

#define REP(i , j , k)  for(int i = j ; i <  k ; ++i)

#define max3(a,b,c) max(max(a,b), c);

#define min3(a,b,c) min(min(a,b), c);

//priority_queue<int ,vector<int>, greater<int> >que;

const ll mos = 0x7FFFFFFF;  //

const ll nmos = 0x80000000;  //-2147483648

const int inf = 0x3f3f3f3f;

const ll inff = 0x3f3f3f3f3f3f3f3f; //

const int mod = 1e9+;

const double esp = 1e-;

const double PI=acos(-1.0);

const double PHI=0.61803399;    //黄金分割点

const double tPHI=0.38196601;

template<typename T>

inline T read(T&x){

    x=;int f=;char ch=getchar();

    while (ch<''||ch>'') f|=(ch=='-'),ch=getchar();

    while (ch>=''&&ch<='') x=x*+ch-'',ch=getchar();

    return x=f?-x:x;

}

/*-----------------------showtime----------------------*/

            const int maxn = ;

            vector<pii>mp[maxn];

            int n,m;

            int dp[maxn][maxn],a[maxn];

            int dfs(int u, int fa){

                int res = ;

                if(mp[u].size() == ) {

                    dp[u][] = a[u];

                    return ;

                }

                for(int i=; i<mp[u].size(); i++){

                    int v = mp[u][i].fi;

                    if(v == fa) continue;

                    res += dfs(v, u);

                    dp[u][] = ;

                    for(int j=res; j >= ; j--){

                        for(int k=; k<=j; k++){

                            dp[u][j] = max(dp[u][j], dp[u][j-k] + dp[v][k] - mp[u][i].se);

                        }

                    }

                }

                return res;

            }

int main(){

            scanf("%d%d", &n, &m);

            memset(dp, ~inf, sizeof(dp));

            for(int i=; i<=n-m; i++){

                    int k;  scanf("%d", &k);

                    for(int j=; j<=k; j++) {

                        int v,w;

                        scanf("%d%d", &v, &w);

                        mp[i].pb(pii(v,w));

                    }

            }

            for(int i=n-m+; i<=n; i++) scanf("%d", &a[i]);

            int tmp = dfs(,-);

            for(int i=tmp; i>=; i--) {

                if(dp[][i] >= ) {

                    printf("%d\n", i);

                    return ;

                }

            }

            return ;

}