#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e4 + 10, maxm = 5e5, inf = 0x3f3f3f3f;
int hea[maxn], nxt[maxm], to[maxm], w[maxm], cur[maxn], d[maxn], q[maxn], S, T,
    tot, n, m;
void ins(int a, int b, int c) {
  nxt[++tot] = hea[a];
  hea[a] = tot;
  to[tot] = b;
  w[tot] = c;
}
void add(int a, int b, int c) {
  ins(a, b, c);
  ins(b, a, 0);
}
int dfs(int x, int f) {
  if (x == T) return f;
  int sum = 0;
  for (int &i = cur[x]; i && f; i = nxt[i])
    if (d[to[i]] == d[x] + 1 && w[i]) {
      int t = dfs(to[i], min(f, w[i]));
      w[i] -= t, w[i ^ 1] += t;
      sum += t, f -= t;
    }
  return sum;
}
int bfs() {
  int H = 1, E = 1;
  memset(d, 0, sizeof(d));
  d[q[H = E = 1] = S] = 1;
  while (H <= E) {
    int x = q[H++];
    for (int i = hea[x]; i; i = nxt[i])
      if (w[i] && !d[to[i]]) d[q[++E] = to[i]] = d[x] + 1;
  }
  return d[T];
}
int a[maxm], b[maxm], c[maxm];
int check(int mid) {
  S = n << 1 | 1, T = S + 1;
  tot = 1;
  memset(hea, 0, sizeof(hea));
  for (int i = 1; i <= n; i++) add(S, i, 1), add(i + n, T, 1);
  for (int i = 1; i <= m; i++)
    if (c[i] <= mid) add(a[i], b[i] + n, 1);
  int sum = 0;
  while (bfs()) {
    memcpy(cur, hea, sizeof(cur));
    sum += dfs(S, inf);
  }
  return sum == n;
}
int main() {
  int L = 1e9, R = 0, fl = 0;
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= m; i++) {
    scanf("%d%d%d", a + i, b + i, c + i);
    L = min(L, c[i]);
    R = max(R, c[i]);
  }
  while (L <= R) {
    int mid = (L + R) >> 1;
    if (check(mid))
      R = mid - 1, fl = 1;
    else
      L = mid + 1;
  }
  if (fl)
    printf("%d\n", R + 1);
  else
    puts("-1");
  return 0;
}
