#include <bits/stdc++.h>
using namespace std;
int main() {
  char s[110];
  int k, n;
  scanf("%s%d%d%*c", s, &k, &n);
  int l = strlen(s);
  for (int i = 0; i < l; i++) s[i] -= 'a';
  int b[26][26] = {0};
  for (int i = 0; i < n; i++) {
    char x, y;
    int c;
    scanf("%c %c %d%*c", &x, &y, &c);
    b[x - 'a'][y - 'a'] = c;
  }
  int f[110][110][26];
  memset(f, 0x80, sizeof(f));
  for (int i = 0; i < 26; i++) f[0][(i != s[0])][i] = 0;
  for (int i = 1; i < l; i++)
    f[i][0][s[i]] = f[i - 1][0][s[i - 1]] + b[s[i - 1]][s[i]];
  for (int i = 1; i < l; i++) {
    for (int j = 1; j <= k; j++) {
      for (int c = 0; c < 26; c++) {
        for (int d = 0; d < 26; d++) {
          f[i][j][c] = max(f[i][j][c], f[i - 1][j - (c != s[i])][d] + b[d][c]);
        }
      }
    }
  }
  int maxb = 0x80000000;
  for (int i = 0; i <= k; i++)
    for (int j = 0; j < 26; j++) maxb = max(maxb, f[l - 1][i][j]);
  printf("%d\n", maxb);
}
