#include <bits/stdc++.h>
using namespace std;
const int N = 205;
long long dp[N][N][30];
long long m[26][26];
void solve() {
  string s;
  int k, n, f;
  cin >> s >> k >> f;
  n = (int)s.size();
  for (int i = 0; i < f; i++) {
    char a, b;
    long long x;
    cin >> a >> b >> x;
    m[a - 'a'][b - 'a'] = x;
  }
  for (int i = 0; i <= 200; i++)
    for (int j = 0; j <= 200; j++)
      for (int c = 0; c < 26; c++) dp[i][j][c] = -1e14;
  for (int c = 0; c < 26; c++) {
    if (c == (s[0] - 'a')) {
      dp[0][0][c] = 0;
    } else
      dp[0][1][c] = 0;
  }
  for (int i = 1; i < n; i++) {
    for (int j = 0; j <= k; j++) {
      for (int cur_c = 0; cur_c < 26; cur_c++) {
        for (int prev_c = 0; prev_c < 26; prev_c++) {
          int add = (cur_c != (s[i] - 'a'));
          if (add + j <= k) {
            dp[i][add + j][cur_c] = max(
                dp[i][add + j][cur_c], dp[i - 1][j][prev_c] + m[prev_c][cur_c]);
          }
        }
      }
    }
  }
  long long ans = INT_MIN;
  for (int j = 0; j <= k; j++)
    for (int c = 0; c < 26; c++) ans = max(ans, dp[n - 1][j][c]);
  cout << ans << '\n';
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ;
  int t = 1;
  while (t--) {
    solve();
  }
}
