#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:136777216")
using namespace std;
int bits(int x) { return x == 0 ? 0 : 1 + bits(x & (x - 1)); }
int v[30][30];
int dp[2][26][111];
int main() {
  const int ninf = -1000000;
  for (int(i) = 0; (i) < (30); (i)++)
    for (int(j) = 0; (j) < (30); (j)++) v[i][j] = 0;
  string s;
  int K, m;
  cin >> s >> K >> m;
  int n = (int)(s).size();
  K = min(K, n);
  char a, b;
  int c;
  for (int(i) = 0; (i) < (m); (i)++) {
    cin >> a >> b >> c;
    v[a - 'a'][b - 'a'] = c;
  }
  for (int(j) = 0; (j) < (26); (j)++)
    for (int(k) = 0; (k) < (K + 1); (k)++) dp[0][j][k] = ninf;
  for (int(j) = 0; (j) < (26); (j)++)
    if (j == s[0] - 'a')
      dp[0][j][0] = 0;
    else
      dp[0][j][1] = 0;
  int add;
  for (int i = 1; i < n; i++) {
    int now = i % 2, bef = 1 - now;
    for (int(j) = 0; (j) < (26); (j)++)
      for (int(k) = 0; (k) < (K + 1); (k)++) dp[now][j][k] = ninf;
    for (int(prev) = 0; (prev) < (26); (prev)++)
      for (int(cur) = 0; (cur) < (26); (cur)++) {
        if (cur == s[i] - 'a')
          add = 0;
        else
          add = 1;
        if (add == 0)
          dp[now][cur][0] =
              max(dp[now][cur][0], dp[bef][prev][0] + v[prev][cur]);
        for (int(ch) = (1); (ch) < (K + 1); (ch)++) {
          dp[now][cur][ch] =
              max(dp[now][cur][ch], dp[bef][prev][ch - add] + v[prev][cur]);
        }
      }
  }
  int r = ninf, t = (n - 1) % 2;
  for (int(j) = 0; (j) < (26); (j)++)
    for (int(k) = 0; (k) < (K + 1); (k)++) r = max(r, dp[t][j][k]);
  cout << r;
  return 0;
}
