import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


enum INF = 10L^^18;

void main() {
  try {
    for (; ; ) {
      const T = readInt();
      const N = readInt();
      const M = readInt();
      auto A = new int[M];
      auto B = new int[M];
      auto C = new long[M];
      foreach (i; 0 .. M) {
        A[i] = readInt() - 1;
        B[i] = readInt() - 1;
        C[i] = readLong();
      }
      
      auto G = new int[][N];
      foreach (i; 0 .. M) {
        if (T == 0) {
          G[A[i]] ~= i;
          G[B[i]] ~= i;
        } else {
          G[A[i]] ~= i;
        }
      }
      
      long ans = INF;
      foreach (i0; 0 .. M) {
        alias Entry = Tuple!(long, "c", int, "u");
        BinaryHeap!(Array!Entry, "a.c > b.c") que;
        auto dist = new long[N];
        dist[] = INF;
        dist[B[i0]] = 0;
        que.insert(Entry(0, B[i0]));
        for (; !que.empty; ) {
          const c = que.front.c;
          const u = que.front.u;
          que.removeFront;
          if (dist[u] == c) {
            if (u == A[i0]) {
              chmin(ans, C[i0] + c);
              break;
            }
            foreach (i; G[u]) {
              if (i != i0) {
                const cc = c + C[i];
                const v = A[i] ^ B[i] ^ u;
                if (chmin(dist[v], cc)) {
                  que.insert(Entry(cc, v));
                }
              }
            }
          }
        }
      }
      writeln((ans >= INF) ? -1 : ans);
    }
  } catch (EOFException e) {
  }
}