#include <bits/stdc++.h>
using namespace std;
const int inf = 1e6;
const double eps = 1e-7;
const int maxn = 1e6 + 55;
const int maxk = 320;
const int base = 1e9 + 7;
const long long basell = 1e18 + 3;
const long double PI = acos(-1.0);
string itosm(long long x) {
  if (x == 0) return "0";
  string ans = "";
  while (x > 0) {
    ans += ((x % 10) + '0');
    x /= 10;
  }
  reverse(ans.begin(), ans.end());
  return ans;
}
long long stoim(string str) {
  long long ans = 0;
  long long k = 1;
  for (int i = str.length() - 1; i >= 0; i--) {
    ans += (str[i] - '0') * k;
    k *= 10;
  }
  return ans;
}
vector<pair<int, int> > g[100];
int dp[100][100][100];
void inline solve() {
  int n, k, m;
  cin >> n >> k >> m;
  for (int i = 0; i < m; i++) {
    int u, v, cost;
    cin >> u >> v >> cost;
    g[u].push_back(make_pair(v, cost));
  }
  for (int i = 0; i <= n; i++)
    for (int j = 0; j <= n; j++)
      for (int g = 0; g <= k; g++) dp[i][j][g] = inf;
  for (int i = 0; i <= n; i++) dp[i][n][1] = dp[i][1][1] = 0;
  for (int cnt = 1; cnt < k; cnt++) {
    for (int v = 1; v <= n; v++) {
      for (int i = 1; i <= n; i++) {
        if (i == v || dp[v][i][cnt] == inf) continue;
        if (i < v) {
          for (pair<int, int> to : g[v])
            if (i <= to.first && to.first < v) {
              dp[to.first][i][cnt + 1] =
                  min(dp[to.first][i][cnt + 1], dp[v][i][cnt] + to.second);
              dp[to.first][v - 1][cnt + 1] =
                  min(dp[to.first][v - 1][cnt + 1], dp[v][i][cnt] + to.second);
            }
        } else {
          for (pair<int, int> to : g[v])
            if (v < to.first && to.first <= i) {
              dp[to.first][i][cnt + 1] =
                  min(dp[to.first][i][cnt + 1], dp[v][i][cnt] + to.second);
              dp[to.first][v + 1][cnt + 1] =
                  min(dp[to.first][v + 1][cnt + 1], dp[v][i][cnt] + to.second);
            }
        }
      }
    }
  }
  int ans = inf;
  for (int i = 0; i <= n; i++)
    for (int j = 0; j <= n; j++) ans = min(ans, dp[i][j][k]);
  if (inf == ans) ans = -1;
  cout << ans;
}
int main() {
  ios_base::sync_with_stdio(0);
  ;
  solve();
  return 0;
}
