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#include<iostream>
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#include<string>
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#include<string.h>
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#include<vector>
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#include<queue>
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#include<map>
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#include<stack>
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#include<set>
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#include<functional>
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#include<utility>
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#include<algorithm>
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#include<cmath>
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#include<climits>
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#include<tuple>
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#include<numeric>
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#include<any>
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#include<bitset>
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#define int long long
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using namespace std;
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const int N = 1e3 + 10;
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int n, m, tx, ty, tt, ans;
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vector<int> fa;
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multiset<tuple<int, int, int>> mul;//t,x,y
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int find(int u) {
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  if (fa[u] != u) fa[u] = find(fa[u]);
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  return fa[u];
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}
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signed main() {
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  cin.tie(nullptr)->ios::sync_with_stdio(false);
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  cin >> n >> m;
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  fa.resize(n + 10);
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  iota(fa.begin(), fa.end(), 0);
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  while (m--) cin >> tx >> ty >> tt, mul.insert(make_tuple(tt, tx, ty));
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  while (!mul.empty()) {
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    auto [t, x, y] = *(mul.begin());
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    mul.erase(mul.begin());
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    int fx = find(x), fy = find(y);
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    if (fx != fy) fa[fx] = fy, ans = max(ans, t);
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  }
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  for (int i = 1;i <= n;i++)
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    if (find(i) != find(1)) {
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      cout << -1;
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      return 0;
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    }
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  cout << ans;
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  return 0;
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}