#include <bits/stdc++.h>
using namespace std;
template <typename T>
void get_int(T &x) {
  char t = getchar();
  bool neg = false;
  x = 0;
  for (; (t > '9' || t < '0') && t != '-'; t = getchar())
    ;
  if (t == '-') neg = true, t = getchar();
  for (; t <= '9' && t >= '0'; t = getchar()) x = x * 10 + t - '0';
  if (neg) x = -x;
}
template <typename T>
void print_int(T x) {
  if (x < 0) putchar('-'), x = -x;
  short a[20] = {}, sz = 0;
  while (x > 0) a[sz++] = x % 10, x /= 10;
  if (sz == 0) putchar('0');
  for (int i = sz - 1; i >= 0; i--) putchar('0' + a[i]);
}
const int inf = 0x3f3f3f3f;
const long long Linf = 1ll << 61;
const double pi = acos(-1.0);
int n, m, k, eu[100111], ev[100111], el[100111];
bool store[100111];
int main() {
  get_int(n), get_int(m), get_int(k);
  for (int i = 1; i <= m; i++) get_int(eu[i]), get_int(ev[i]), get_int(el[i]);
  for (int i = 1, x; i <= k; i++) {
    get_int(x);
    store[x] = 1;
  }
  int ans = inf;
  for (int i = 1; i <= m; i++)
    if (store[eu[i]] != store[ev[i]]) ans = min(ans, el[i]);
  if (ans == inf) ans = -1;
  print_int(ans), puts("");
  return 0;
}
