#include <bits/stdc++.h>
using namespace std;
const int N = 101;
const int A = 30;
const int I = 1e9;
string s;
int dp[N][N][A];
int lkp[A][A];
int n, k;
int solve(int x, int y, int lst) {
  if (x == n) return 0;
  int &res = dp[x][y][lst];
  if (res != -1) return res;
  res = -I;
  if (lst == 27) {
    for (int i = 0; i < 26; ++i)
      if (s[x] - 'a' == i)
        res = max(res, solve(x + 1, y, i));
      else if (y > 0)
        res = max(res, solve(x + 1, y - 1, i));
    return res;
  }
  for (int i = 0; i < 26; ++i)
    if (s[x] - 'a' == i) {
      if (lkp[lst][i] != I)
        res = max(res, solve(x + 1, y, i) + lkp[lst][i]);
      else
        res = max(res, solve(x + 1, y, i));
    } else if (y > 0) {
      if (lkp[lst][i] != I)
        res = max(res, solve(x + 1, y - 1, i) + lkp[lst][i]);
      else
        res = max(res, solve(x + 1, y - 1, i));
    }
  return res;
}
int main() {
  cin >> s >> k >> n;
  for (int i = 0; i < A; ++i)
    for (int j = 0; j < A; ++j) lkp[i][j] = I;
  for (int i = 0; i < n; ++i) {
    char a, b;
    int x;
    cin >> a >> b >> x;
    a -= 'a';
    b -= 'a';
    lkp[a][b] = x;
  }
  memset(dp, -1, sizeof(dp));
  n = s.length();
  cout << solve(0, k, 27) << "\n";
}
