#include <bits/stdc++.h>
using namespace std;
const int inf = (int)1e9 * 2;
int n, m, ind;
long long L[55], M[55], R[55], A[55], ans = -inf, un;
bool all = 1;
vector<int> a[55];
void calc() {
  for (int i = 0; i < n; i++) {
    R[i] = M[i] = L[i] = -inf;
    for (int j = 0; j < a[i].size(); j++) {
      A[i] += (long long)a[i][j];
      if (A[i] > L[i]) L[i] = A[i];
    }
    long long sum = 0;
    for (int j = a[i].size() - 1; j >= 0; j--) {
      sum += (long long)a[i][j];
      if (sum > R[i]) R[i] = sum;
    }
    sum = 0;
    for (int j = 0; j < a[i].size(); j++) {
      sum = max(sum + (long long)a[i][j], (long long)a[i][j]);
      M[i] = max(M[i], sum);
    }
  }
}
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++) {
    int l;
    scanf("%d", &l);
    for (int j = 0; j < l; j++) {
      int x;
      scanf("%d", &x);
      a[i].push_back(x);
    }
  }
  calc();
  for (int i = 0; i < m; i++) {
    scanf("%d", &ind), ind--;
    ans = max(un + L[ind], ans);
    un = max(un + A[ind], R[ind]);
    ans = max(ans, M[ind]);
  }
  printf("%I64d\n", ans);
  return 0;
}
