#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 10;
const int inf = 1e9;
int to[N], ww[N], nxt[N], tt = 1, s, t, h[N], cur[N], dep[N], u[N], v[N], d[N],
                          st[N], tp, m, n;
void adde(int u, int v, int w) {
  to[++tt] = v;
  ww[tt] = w;
  nxt[tt] = h[u];
  h[u] = tt;
  to[++tt] = u;
  ww[tt] = 0;
  nxt[tt] = h[v];
  h[v] = tt;
}
bool bfs() {
  memset(dep, 0, 4 * (t + 1));
  queue<int> q;
  q.push(s);
  dep[s] = 1;
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    for (int i = h[u], v; v = to[i], i; i = nxt[i])
      if (!dep[v] && ww[i]) {
        dep[v] = dep[u] + 1;
        q.push(v);
        if (v == t) return 1;
      }
  }
  return 0;
}
int dfs(int u, int flow) {
  if (u == t) return flow;
  int ret = 0;
  for (int &i = cur[u], v; v = to[i], i; i = nxt[i])
    if (dep[v] == dep[u] + 1 && ww[i]) {
      int d = dfs(v, min(flow, ww[i]));
      ww[i] -= d;
      ww[i ^ 1] += d;
      ret += d;
      flow -= d;
      if (!flow) break;
    }
  return ret;
}
int dinic() {
  int ret = 0;
  while (bfs()) {
    memcpy(cur, h, 4 * (t + 1));
    ret += dfs(s, inf);
  }
  return ret;
}
bool check(int mid) {
  tt = 1;
  memset(h, 0, 4 * (t + 1));
  for (int i = 1; i <= n; i++) adde(s, i, 1), adde(i + n, t, 1);
  for (int i = 1; i <= m; i++)
    if (d[i] <= mid) adde(u[i], v[i] + n, 1);
  return dinic() == n;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> m;
  s = 0;
  t = n + n + 1;
  for (int i = 1; i <= m; i++) cin >> u[i] >> v[i] >> d[i], st[++tp] = d[i];
  sort(st + 1, st + tp + 1);
  tp = unique(st + 1, st + tp + 1) - st - 1;
  int l = 1, r = tp + 1;
  while (l < r) {
    int mid = (l + r) >> 1;
    if (check(st[mid]))
      r = mid;
    else
      l = mid + 1;
  }
  if (l == tp + 1)
    cout << -1;
  else
    cout << st[l];
  return 0;
}
