#include <bits/stdc++.h>
using namespace std;
const int inf = 1000 * 1000 * 1000;
string S;
vector<vector<int> > G;
vector<vector<vector<int> > > DP, U;
int n, k;
int F(int pos, int k, int let) {
  if (k < 0) return -inf;
  if (pos == S.size() - 1) return 0;
  if (DP[pos][k][let] == -inf) {
    int res = DP[pos][k][let];
    if (k)
      for (int i = 0; i < 26; ++i)
        res = max(res, F(pos + 1, k - 1, i) + G[let][i]);
    res = max(res, F(pos + 1, k, S[pos + 1] - 'a') + G[let][S[pos + 1] - 'a']);
    DP[pos][k][let] = res;
  }
  return DP[pos][k][let];
}
int main() {
  cin >> S >> k;
  cin >> n;
  DP.resize(1 << 7, vector<vector<int> >(1 << 7, vector<int>(1 << 5, -inf)));
  U.resize(1 << 7, vector<vector<int> >(1 << 7, vector<int>(1 << 5, -inf)));
  string st;
  G.resize(26, vector<int>(26, 0));
  for (int i = 0; i < n; ++i) {
    cin >> st;
    int b = st[0] - 'a';
    cin >> st;
    int f = st[0] - 'a';
    cin >> G[b][f];
  }
  int res = -inf;
  for (int i = 0; i < 26; ++i) res = max(res, F(0, k - 1, i));
  cout << max(res, F(0, k, S[0] - 'a'));
  return 0;
}
