#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

#include <algorithm>
#include <bitset>
#include <climits>
#include <cmath>
#include <cstring>
#include <deque>
#include <forward_list>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;
typedef long long ll;
typedef pair<ll, int> P;
typedef bitset<16> BS;
struct edge {
    int from, to, id;
    ll cost;
};
const ll MOD = 1E+09 + 7;
const ll INF = 1E18;
const int MAX_N = 2000;

int T, N, M;

vector<edge> G[MAX_N + 1];
ll d[MAX_N + 1];
edge E[MAX_N + 1];

void dijkstra(int s, int nid);

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    cin >> T >> N >> M;

    for (int i = 1; i <= M; i++) {
        int u, v;
        ll w;
        cin >> u >> v >> w;
        G[u].push_back(edge { u, v, i, w });
        if (T == 0) {
            G[v].push_back(edge { v, u, i, w });
        }
        E[i] = edge { u, v, i, w };
    }

    ll ans = INF;
    for (int id = 1; id <= M; id++) {
        fill(d + 1, d + N + 1, INF);
        int from = E[id].from, to = E[id].to;
        ll c = E[id].cost;
        dijkstra(to, id);
        ans = min(ans, d[from] + c);
    }

    /*
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < N; j++) {
            cout << "i = " << i << ", j = " << j << ", dp = " << dp[i][j] << "\n";
        }
    }
    */

    if (ans == INF) {
        cout << -1 << "\n";
    } else {
        cout << ans << "\n";
    }

    return 0;
}

void dijkstra(int s, int nid)
{
    priority_queue<P, vector<P>, greater<P>> que;
    que.push(P(0, s));
    d[s] = 0;
    while (!que.empty()) {
        P p = que.top();
        int v = p.second;
        que.pop();
        if (d[v] < p.first)
            continue; //被った頂点に関しては更新前の古いデータはとばす
        for (int i = 0; i < G[v].size(); i++) {
            edge e = G[v][i];
            if (d[e.to] > d[v] + e.cost && e.id != nid) {
                d[e.to] = d[v] + e.cost;
                que.push(P(d[e.to], e.to));
            }
        }
    }
}