为什么WA？玄关

#include<bits/stdc++.h>
#define int long long
#define ll long long
#define ull unsigned long long
#define i128 __int128
#define inf (1ll << 62)
#define PII pair<int, int>
#define fi first
#define se second
#define pb push_back
using namespace std;
const int MAXN = 2e5 + 10;
int h, w, n;
struct Node {
	int x, y;
};
vector<Node> d(MAXN);

namespace DSU {
	vector<int> fa(MAXN);
	void Init(int n) {for (int i = 0; i <= n; i++) fa[i] = i;}
	int find(int x) {return fa[x] == x ? x : fa[x] = find(fa[x]);}
	void merge(int a, int b) {int x = find(a), y = find(b);fa[x] = y;}
}

using namespace DSU;

bool check(int x) {
	Init(n);
	int pos = -1;
	for (int i = 0; i < n; i++) {
		if (d[i].y == d[0].y + 1) {
			pos = i;
			break;
		}
	}
	for (int i = 0; i < n - 1; i++) {
		if (d[i + 1].y == d[i].y) {
			if (d[i + 1].x - d[i].x <= x && find(i + 1) != find(i)) {
				merge(i + 1, i);
			}
		}
		if (pos != -1) {
			while (pos < n && (d[pos].x < d[i].x || d[pos].y < d[i].y + 1)) pos++;
			while (pos < n && d[pos].x <= d[i].x + x && d[pos].y == d[i].y + 1) {
				if (find(pos) != find(i)) {
					merge(pos, i);
				}
				pos++;
			}	
		}
	}
	int num = find(0);
	for (int i = 1; i < n; i++) {
		if (find(i) != num) {
			return false;
		}
	}
	return true;
}

void solve() {
	cin >> h >> w >> n;
	for (int i = 0; i < n; i++) {
		cin >> d[i].x >> d[i].y;
	}
	sort(d.begin(), d.begin() + n, [&](Node a, Node b) {
		if (a.y != b.y) return a.y < b.y;
		return a.x < b.x;
	});
	int l = 0, r = 1e14;
	while (l < r) {
		int mid = (l + r) >> 1;
		if (check(mid)) r = mid;
		else l = mid + 1;
	}
	if (!check(l)) cout << "-1\n";
	else cout << l << "\n";
}

signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int t = 1;
	while (t--) {
		solve();
	}
	return 0;
}