#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  int k, n;
  cin >> s >> k >> n;
  map<pair<char, char>, int> pairs;
  for (int i = 0; i < n; ++i) {
    char x, y;
    int c;
    cin >> x >> y >> c;
    pairs[make_pair(x, y)] = c;
  }
  vector<vector<vector<int> > > a(s.size());
  for (int i = 0; i < a.size(); ++i) {
    a[i].resize(k + 1);
    for (int j = 0; j <= k; ++j) {
      a[i][j].assign(26, -100000000);
    }
  }
  a[0][0][s[0] - 'a'] = 0;
  if (k > 0) {
    for (int l = 0; l < 26; ++l) {
      if ('a' + l != s[0]) {
        a[0][1][l] = 0;
      }
    }
  }
  for (int i = 1; i < a.size(); ++i) {
    a[i][0][s[i] - 'a'] =
        a[i - 1][0][s[i - 1] - 'a'] + pairs[make_pair(s[i - 1], s[i])];
    for (int j = 1; j <= min(i + 1, k); ++j) {
      for (int l = 0; l < 26; ++l) {
        int maximum = -10000000000;
        for (int t = 0; t < 26; ++t) {
          if ((l + 'a' == 'o') && (t + 'a' == 'l')) {
            i = i;
          }
          if ('a' + l == s[i]) {
            maximum = max(maximum,
                          a[i - 1][j][t] + pairs[make_pair('a' + t, 'a' + l)]);
          } else {
            maximum = max(maximum, (a[i - 1][j - 1][t] +
                                    pairs[make_pair('a' + t, 'a' + l)]));
          }
        }
        a[i][j][l] = maximum;
      }
    }
  }
  int maximum = -1000000000;
  for (int j = 0; j <= k; ++j) {
    for (int l = 0; l < 26; ++l) {
      maximum = max(maximum, a[a.size() - 1][j][l]);
    }
  }
  cout << maximum;
  return 0;
}
