#include <bits/stdc++.h>
using namespace std;
int n, m, ans = -1, vis1[10005], vis2[10005];
struct node {
  int u, v, d;
} a[100005];
bool check(int x) {
  int sum1 = 0, sum2 = 0;
  memset(vis1, 0, sizeof(vis1));
  memset(vis2, 0, sizeof(vis2));
  for (int i = 1; i <= m; i++) {
    if (a[i].d <= x) {
      if (vis1[a[i].v] == 0) sum1++;
      if (vis2[a[i].u] == 0) sum2++;
      vis1[a[i].v] = 1;
      vis2[a[i].u] = 1;
    }
  }
  if (sum1 != n || sum1 != sum2) return false;
  return true;
}
int main() {
  int l = 0, r = 0;
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= m; i++) {
    scanf("%d%d%d", &a[i].u, &a[i].v, &a[i].d);
    r = max(r, a[i].d);
  }
  while (l <= r) {
    int mid = (l + r) >> 1;
    if (check(mid) == true) {
      ans = mid;
      r = mid - 1;
    } else
      l = mid + 1;
  }
  printf("%d", ans);
  return 0;
}
