#include <bits/stdc++.h>
using namespace std;
string s;
const int inf = -(1 << 30);
int i, k, n, c[30][30], ans, r;
char x, y;
int dp[111][30][111], us[111][30][111];
int DP(int p, char t, int k) {
  if (p >= s.size() - 1) return 0;
  if (us[p][t - 'a'][k] != 0) return dp[p][t - 'a'][k];
  us[p][t - 'a'][k] = 1;
  int ans = inf;
  for (char t1 = 'a'; t1 <= 'z'; t1++) {
    if (t1 == s[p + 1])
      ans = max(ans, DP(p + 1, t1, k) + c[t - 'a'][t1 - 'a']);
    else if (k > 0)
      ans = max(ans, DP(p + 1, t1, k - 1) + c[t - 'a'][t1 - 'a']);
  }
  dp[p][t - 'a'][k] = ans;
  return ans;
}
int main() {
  cin >> s >> r >> n;
  for (i = 0; i < n; i++) {
    cin >> x >> y >> k;
    c[x - 'a'][y - 'a'] = k;
  }
  ans = inf;
  for (char t1 = 'a'; t1 <= 'z'; t1++) {
    if (s[0] == t1)
      ans = max(ans, DP(0, t1, r));
    else if (r > 0)
      ans = max(ans, DP(0, t1, r - 1));
  }
  cout << ans;
  return 0;
}
