#include <bits/stdc++.h>
using namespace std;
int inf = 1000000000;
int dp[105][105][26], K, c[26][26];
char s[105], trace[105][105][26];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> (s + 1) >> K;
  int N = strlen(s + 1);
  int n;
  cin >> n;
  while (n--) {
    char x, y;
    cin >> x >> y;
    int l;
    cin >> l;
    c[x - 'a'][y - 'a'] += l;
  }
  for (int i = 1; i <= N; i++)
    for (int j = 0; j <= K; j++)
      for (int h = 0; h < 26; h++) dp[i][j][h] = -inf;
  for (int j = 0; j <= K; j++) {
    for (int h = 0; h < 26; h++) {
      if ((j == 1 and (s[1] - 'a') != h) or (j == 0 and (s[1] - 'a') == h)) {
        dp[1][j][h] = 0;
      } else
        dp[1][j][h] = -inf;
    }
  }
  for (int i = 2; i <= N; i++) {
    for (int j = 0; j <= K; j++) {
      if (!j) {
        for (int h = 0; h < 26; h++) {
          if (h != (s[i] - 'a'))
            dp[i][j][h] = -inf;
          else
            dp[i][j][h] = dp[i - 1][j][s[i - 1] - 'a'] + c[s[i - 1] - 'a'][h];
        }
        continue;
      }
      for (int h = 0; h < 26; h++) {
        if (h == (s[i] - 'a')) {
          for (int o = 0; o < 26; o++)
            dp[i][j][h] = max(dp[i][j][h], dp[i - 1][j][o] + c[o][h]);
        } else {
          for (int o = 0; o < 26; o++) {
            dp[i][j][h] = max(dp[i][j][h], dp[i - 1][j - 1][o] + c[o][h]);
          }
        }
      }
    }
  }
  int mx = -inf;
  for (int j = 0; j <= K; j++) {
    for (int h = 0; h < 26; h++)
      if (dp[N][j][h] > mx) mx = dp[N][j][h];
  }
  cout << mx << '\n';
  return 0;
}
