#include <bits/stdc++.h>
using namespace std;
long long int gcd(long long int a, long long int b) {
  return (!b) ? a : gcd(b, a % b);
}
int k1, n;
int val[26][26];
string s;
int dp[101][101][26];
void solve() {
  cin >> s >> k1 >> n;
  for (int i = 1; i <= n; i++) {
    char x, y;
    cin >> x >> y >> val[x - 'a'][y - 'a'];
  }
  int ns = (int)s.size();
  for (int i = 0; i <= ns; i++) {
    for (int k = 0; k <= k1; k++) {
      for (int c = 0; c <= 25; c++) dp[i][k][c] = -1e8;
    }
  }
  for (int i = 0; i <= 25; i++) dp[1][1][i] = 0;
  dp[1][0][s[0] - 'a'] = 0;
  for (int i = 2; i <= (int)s.size(); i++) {
    for (int c = 0; c <= 25; c++) {
      int p = (s[i - 1] - 'a' != c);
      for (int k = p; k <= k1; k++) {
        for (int c1 = 0; c1 <= 25; c1++)
          dp[i][k][c] = max(dp[i][k][c], dp[i - 1][k - p][c1] + val[c1][c]);
      }
    }
  }
  int ans = -1e8;
  for (int i = 0; i <= 25; i++) {
    for (int k = 0; k <= k1; k++) {
      ans = max(ans, dp[(int)s.size()][k][i]);
    }
  }
  cout << ans;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  if (fopen("input.txt", "r")) {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
  }
  int t = 1;
  while (t--) {
    solve();
  }
}
