#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:16777216")
using namespace std;
const double PI = 2 * acos(0.0);
const double EPS = 1e-12;
const int INF = 100000000;
string s;
char x, y;
int bon[26][26];
int k, m, c;
int d[100][26][101];
int main() {
  cin >> s >> k >> m;
  for (int i = (int)(0); i < (int)(m); ++i) {
    cin >> x >> y >> c;
    bon[x - 'a'][y - 'a'] = c;
  };
  for (int i = (int)(0); i < (int)(26); ++i)
    for (int j = (int)(0); j < (int)(101); ++j) d[0][i][j] = -INF;
  d[0][s[0] - 'a'][0] = 0;
  for (int i = (int)(0); i < (int)(26); ++i)
    if (i != s[0] - 'a') d[0][i][1] = 0;
  for (int i = 1; i < s.size(); ++i)
    for (int last = 0; last < 26; ++last)
      for (int ch = 0; ch <= k; ++ch) {
        d[i][last][ch] = -INF;
        if (last == s[i] - 'a')
          for (int kk = (int)(0); kk < (int)(26); ++kk)
            d[i][last][ch] =
                max(d[i][last][ch], d[i - 1][kk][ch] + bon[kk][last]);
        else if (ch)
          for (int kk = (int)(0); kk < (int)(26); ++kk)
            d[i][last][ch] =
                max(d[i][last][ch], d[i - 1][kk][ch - 1] + bon[kk][last]);
      };
  int ans = -INF;
  for (int i = (int)(0); i < (int)(26); ++i)
    for (int j = (int)(0); j < (int)(k + 1); ++j)
      ans = max(ans, d[s.size() - 1][i][j]);
  cout << ans;
  return 0;
};
