#include <bits/stdc++.h>
using namespace std;
const long long lenmax = 105;
const long long neg_inf = -1000000;
int bonuses[26][26];
int dp[lenmax][26][lenmax];
string check;
int change(int n) {
  int max_profit;
  int pos;
  char letter;
  int cur_profit;
  for (int k = 0; k <= n; k++) {
    for (char j = 'a'; j <= 'z'; j++) {
      dp[0][j - 'a'][k] = neg_inf;
    }
  }
  for (char j = 'a'; j <= 'z'; j++) {
    if (check[0] == j) {
      dp[0][j - 'a'][0] = 0;
    } else {
      dp[0][j - 'a'][1] = 0;
    }
  }
  for (int i = 1; i < check.length(); i++) {
    for (char j = 'a'; j <= 'z'; j++) {
      for (int k = 0; k <= n; k++) {
        if (k == 0 && check[i] != j) {
          dp[i][j - 'a'][k] = neg_inf;
          continue;
        }
        max_profit = neg_inf;
        for (char d = 'a'; d <= 'z'; d++) {
          max_profit =
              max(max_profit, dp[i - 1][d - 'a'][k - (bool)(check[i] != j)] +
                                  bonuses[d - 'a'][j - 'a']);
        }
        dp[i][j - 'a'][k] = max_profit;
      }
    }
  }
  max_profit = neg_inf;
  for (char j = 'a'; j <= 'z'; j++) {
    for (int k = 0; k <= n; k++) {
      max_profit = max(max_profit, dp[check.length() - 1][j - 'a'][k]);
    }
  }
  return max_profit;
}
int main() {
  cin >> check;
  int k;
  cin >> k;
  int n;
  cin >> n;
  char first, second;
  int amount;
  for (int i = 0; i < 26; i++) {
    for (int j = 0; j < 26; j++) {
      bonuses[i][j] = 0;
    }
  }
  for (int i = 0; i < n; i++) {
    cin >> first >> second >> amount;
    bonuses[first - 'a'][second - 'a'] = amount;
  }
  cout << change(k);
  return 0;
}
