#include <bits/stdc++.h>
using namespace std;
struct Fast {
  Fast() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  }
} fast;
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T& val) {
  std::fill((T*)array, (T*)(array + N), val);
}
long long mod = 1000000007;
long long modpow(long long m, long long n) {
  if (n == 0) return 1;
  if (n % 2 == 0) {
    long long t = modpow(m, n / 2);
    return t * t % mod;
  } else {
    return modpow(m, n - 1) * m % mod;
  }
}
long long power(long long m, long long n) {
  if (n == 0) return 1;
  if (n % 2 == 0) {
    long long t = modpow(m, n / 2);
    return t * t;
  } else {
    return modpow(m, n - 1) * m;
  }
}
long long moddiv(long long a, long long b) {
  return (a * modpow(b, mod - 2)) % mod;
}
const long long INF = 1LL << 60;
string change_binary(long long a) {
  string ret;
  for (int i = 31; i >= 0; i--) {
    ret += (a >> i & 1) + '0';
  }
  return ret;
}
long long nCkmod(long long n, long long k) {
  long long denomi = 1;
  for (int i = n; i > n - k; i--) {
    denomi *= i;
    denomi %= mod;
  }
  long long numera = 1;
  for (long long i = 0; i < (k); i++) {
    numera *= (i + 1);
    numera %= mod;
  }
  return moddiv(denomi, numera);
}
vector<vector<long long>> graph;
long long memo[201][270][201];
string s;
long long n;
map<pair<char, char>, long long> cnt;
long long func(long long row, char alp, long long ch) {
  if (row == s.size()) {
    return 0;
  }
  if (memo[row][alp][ch] != -100000000000000LL) {
    return memo[row][alp][ch];
  }
  long long ret = -100000000000000LL;
  for (long long i = 0; i < (26); i++) {
    long long now = -100000000000000LL;
    if (s[row] == i + 'a') {
      now = cnt[{alp, i + 'a'}] + func(row + 1, i + 'a', ch);
    } else if (ch != 0) {
      now = cnt[{alp, i + 'a'}] + func(row + 1, i + 'a', ch - 1);
    }
    ret = max(ret, now);
  }
  memo[row][alp][ch] = ret;
  return memo[row][alp][ch];
}
int main() {
  Fill(memo, -100000000000000LL);
  cin >> s;
  cin >> n;
  long long a;
  cin >> a;
  for (long long i = 0; i < (a); i++) {
    char one, two;
    int point;
    cin >> one >> two >> point;
    cnt[{one, two}] = point;
  }
  cout << func(0, 'A', n) << endl;
}
