#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:64000000")
using namespace std;
int n, k;
string s;
int d[105][105][26];
int b[26][26];
int main() {
  cin >> s >> k;
  n = (int)s.size();
  int m;
  scanf("%d\n", &m);
  for (int i = 0; i < int(m); i++) {
    char x, y;
    scanf("%c %c", &x, &y);
    x -= 'a';
    y -= 'a';
    scanf("%d\n", &b[x][y]);
  }
  for (int i = 0; i < int(105); i++)
    for (int j = 0; j < int(105); j++)
      for (int c = 0; c < int(26); c++) d[i][j][c] = -1000000009;
  d[0][0][0] = 0;
  for (int i = 0; i < int(n); i++) {
    for (int j = 0; j < int(k + 1); j++) {
      for (int c = 0; c < int(26); c++) {
        if (d[i][j][c] == -1000000009) continue;
        int bonus = b[c][s[i] - 'a'];
        if (i == 0) bonus = 0;
        d[i + 1][j][s[i] - 'a'] =
            max(d[i + 1][j][s[i] - 'a'], d[i][j][c] + bonus);
        if (j < k) {
          for (int c1 = 0; c1 < int(26); c1++) {
            bonus = b[c][c1];
            if (i == 0) bonus = 0;
            d[i + 1][j + 1][c1] = max(d[i + 1][j + 1][c1], d[i][j][c] + bonus);
          }
        }
      }
    }
  }
  int ans = -1000000009;
  for (int j = 0; j < int(k + 1); j++) {
    for (int c = 0; c < int(26); c++) {
      ans = max(ans, d[n][j][c]);
    }
  }
  cout << ans << endl;
  return 0;
}
