#include<iostream>
#include<vector>
#include<string>
#include<set>
#include<map>
#include<algorithm>
#include<queue>
#include<list>
#include<stack>
#include<cstdio>
#include<fstream>
#include<numeric>
#include<functional>
#include<utility>
#include<memory.h>
using namespace std;
using namespace placeholders;
int area[82][82];
int dp[82][82][82][82];
int n, k, m;
int Cal(int left, int right, int cur, int amount){
if (dp[left][right][cur][amount] != -1) return dp[left][right][cur][amount];
if (amount == 1){
dp[left][right][cur][amount] = 0;
return 0;
}
int res = 1e8;
for (int i = 1; i <= n; i++){
if (area[cur][i] <= 1000 && i>left&&i<right){
int l = left, r = right;
if (cur < i) l = cur;
else r = cur;
res = min(res, area[cur][i] + Cal(l, r, i, amount - 1));
}
}
dp[left][right][cur][amount] = res;
return res;
}
int main(){
while (cin >> n >> k){
cin >> m;
for (int i = 1; i <= n; i++)
for (int j = 1; j <= n; j++) area[i][j] = 1e8;
memset(dp, -1, sizeof(dp));
for (int i = 1; i <= m; i++){
int u, v, c;
cin >> u >> v >> c;
area[u][v] = min(area[u][v], c);
}
int ans = 1e8;
for (int i = 1; i <= n; i++){
int left = 0;
int right = n + 1;
ans = min(ans, Cal(left, right, i, k));
}
if (ans >= 1e8) cout << "-1" << endl;
else cout << ans << endl;
}
return 0;
}
