#include <bits/stdc++.h>
using namespace std;
const int big = 1e9;
int dp[83][83][83][83], d[100][100];
int s[100][100][100], s1[100][100][100];
int n, kt, m, u, v, c;
int main() {
  cin >> n >> kt >> m;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) d[i][j] = -1;
  for (int i = 1; i <= m; i++) {
    cin >> u >> v >> c;
    if (d[u][v] == -1)
      d[u][v] = c;
    else
      d[u][v] = min(d[u][v], c);
  }
  for (int k = 1; k <= kt; k++)
    for (int i = 0; i <= n + 1; i++)
      for (int j = 0; j < i; j++)
        for (int l = i + 1; l <= n + 1; l++) dp[k][i][j][l] = -1;
  for (int k = 1; k <= kt; k++)
    for (int i = 0; i <= n + 1; i++)
      for (int j = 0; j <= n + 1; j++) {
        s[k][i][j] = big;
        s1[k][i][j] = big;
      }
  for (int k = 1; k <= kt; k++) {
    for (int i = 1; i <= n; i++)
      for (int j = 0; j < i; j++)
        for (int l = i + 1; l <= n + 1; l++) {
          if (j != 0 || k == 1)
            if (d[j][i] > -1 && s[k - 1][j][l] != big)
              dp[k][i][j][l] = s[k - 1][j][l] + d[j][i];
          if (l != n + 1 || k == 1)
            if (d[l][i] > -1 && s1[k - 1][l][j] != big) {
              if (dp[k][i][j][l] == -1)
                dp[k][i][j][l] = s1[k - 1][l][j] + d[l][i];
              else
                dp[k][i][j][l] = min(dp[k][i][j][l], s1[k - 1][l][j] + d[l][i]);
            }
        }
    for (int i = 1; i <= n; i++)
      for (int j = 0; j < i; j++)
        for (int l = i + 1; l <= n + 1; l++)
          if (dp[k][i][j][l] != -1)
            s[k][i][l] = min(s[k][i][l], dp[k][i][j][l]);
    for (int i = 1; i <= n; i++)
      for (int j = 0; j < i; j++)
        for (int l = i + 1; l <= n + 1; l++)
          if (dp[k][i][j][l] != -1)
            s1[k][i][j] = min(s1[k][i][j], dp[k][i][j][l]);
  }
  int mini = 1e9;
  for (int i = 1; i <= n; i++)
    for (int j = 0; j < i; j++)
      for (int l = i + 1; l <= n + 1; l++)
        if (dp[kt][i][j][l] != -1) mini = min(mini, dp[kt][i][j][l]);
  if (mini == 1e9)
    printf("-1\n");
  else
    printf("%d\n", mini);
  return 0;
}
