#include <bits/stdc++.h>
#define int long long
using namespace std;

void solve() {
	int n;
	cin >> n;

	vector<array<int, 2>> a(n + 1);
	for (int i = 1; i <= n; i++) {
		cin >> a[i][0] >> a[i][1];
	}

	auto check = [&](int v) -> bool {
		set<int> s, r;
		for (int i = 1; i <= n; i++) {
			if (a[i][0] < v) {
				s.insert(-a[i][1] - v);
			} else {
				r.insert(-(a[i][0] + a[i][1]));
			}
		}

		r.insert(1e10);
		r.insert(-1e10);
		for (auto u : s) {
			auto p = prev(r.upper_bound(u));
			if (*p == -1e10) return false;
			else {
				r.erase(p);
			}
		}	
		return true;
	};

	int L = 0, R = 1e9, ans = 0;
	while (L <= R) {
		int mid = (L + R) / 2;
		if (check(mid)) {
			ans = mid;
			L = mid + 1;
		} else {
			R = mid - 1;
		}
	}

	cout << ans << "\n";
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    int T;
    cin >> T;
    while (T--) solve();

    return 0;
}