#include <bits/stdc++.h>
using namespace std;
const int inf = (1 << 30);
int dp[110][700][40], g[35][35];
string s;
int solve(int p, int k, int q) {
  if (p < 0 && k >= 0) return 0;
  if (p < 0 || k < 0) return -inf;
  if (dp[p][k][q] != -1) return dp[p][k][q];
  char ch = q + 'a';
  int ans = -inf;
  for (char curr = 'a'; curr <= 'z'; curr++) {
    int dk = 0;
    if (curr != s[p]) dk++;
    int x = solve(p - 1, k - dk, curr - 'a');
    if (x == -inf) continue;
    ans = max(ans, x + g[curr - 'a'][q]);
  }
  return dp[p][k][q] = ans;
}
int main() {
  fill(&dp[0][0][0], &dp[0][0][0] + 110 * 700 * 40, -1);
  int k;
  cin >> s >> k;
  int t;
  cin >> t;
  for (int i = 0; i < t; i++) {
    string tmp;
    char c1, c2;
    int w;
    cin >> c1 >> c2 >> w;
    g[c1 - 'a'][c2 - 'a'] = w;
  }
  cout << solve(s.size() - 1, k, 30);
  return 0;
}
