#include <bits/stdc++.h>
using namespace std;
int const MAX_SIZE = 110;
int const MAX_K = 110;
int dp[MAX_SIZE][MAX_K][26];
int main() {
  string word;
  int max_k;
  cin >> word >> max_k;
  int n;
  cin >> n;
  map<pair<int, int>, int> t;
  for (int i = (0); i < ((n)); ++i) {
    char a, b;
    int c;
    cin >> a >> b >> c;
    t[make_pair(a - 'a', b - 'a')] = c;
  }
  int const INF = 1e9;
  for (int i = (0); i < ((MAX_SIZE)); ++i)
    for (int j = (0); j < ((MAX_K)); ++j)
      for (int k = (0); k < ((26)); ++k) dp[i][j][k] = -INF;
  for (int i = (0); i < ((26)); ++i) dp[1][i != word[0] - 'a'][i] = 0;
  for (int i = (1); i < ((int)word.size()); ++i)
    for (int j = (0); j < ((max_k + 1)); ++j)
      for (int k1 = (0); k1 < ((26)); ++k1)
        for (int k2 = (0); k2 < ((26)); ++k2)
          if (dp[i][j][k1] != -INF) {
            int cost = 0;
            if (t.count(make_pair(k1, k2))) cost = t[make_pair(k1, k2)];
            int& next = dp[i + 1][j + (k2 != word[i] - 'a')][k2];
            if (next < dp[i][j][k1] + cost) {
              next = dp[i][j][k1] + cost;
            }
          }
  int result = -INF;
  for (int i = (0); i < ((max_k + 1)); ++i)
    for (int j = (0); j < ((26)); ++j)
      result = max(result, dp[(int)word.size()][i][j]);
  cout << result << endl;
  return 0;
}
