#include <bits/stdc++.h>
const long long mod = (long long)1e9 + 7;
const long long ng = -(long long)1e9;
using namespace std;
string str;
long long k, n;
long long val[26][26];
long long dp[102][102][28];
long long p;
long long rec(long long idx, long long c, long long ch) {
  if (dp[idx][c][ch] != ng) return dp[idx][c][ch];
  if (c > k) return dp[idx][c][ch] = INT_MIN;
  if (idx == p) return dp[idx][c][ch] = 0;
  long long mn = INT_MIN;
  for (long long i = 0; i < 26; i++) {
    long long o = (i != str[idx] - 'a' ? 1 : 0);
    long long m = val[ch][i];
    if (idx == 0) m = 0;
    mn = max(mn, m + rec(idx + 1, o + c, i));
  }
  return dp[idx][c][ch] = mn;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> str >> k;
  cin >> n;
  p = str.length();
  memset(val, 0, sizeof(val));
  for (long long i = 0; i < 102; i++) {
    for (long long j = 0; j < 102; j++) {
      for (long long kk = 0; kk < 28; kk++) dp[i][j][kk] = ng;
    }
  }
  for (long long i = 0; i < n; i++) {
    char a, b;
    long long v;
    cin >> a >> b >> v;
    val[a - 'a'][b - 'a'] = v;
  }
  cout << rec(0, 0, str[0] - 'a');
  return 0;
}
