#include <bits/stdc++.h>
using namespace std;
#define int long long
int n,a[2020000],w[2020000];
bool ch(int x){
	vector<int>s;
	for(int i=1;i<=n;i++){
		if(a[i]<x){
			s.push_back(w[i]);}
	}
	sort(s.begin(),s.end());
	for(int i=1;i<=n;i++){	
		if(a[i]<x)continue;
		int t=a[i]-x+w[i];
		auto it=upper_bound(s.begin(),s.end(),t);
		it--;
		if(it!=s.end()&&it>=s.begin()){
			s.erase(it);
		}
		if((int)s.size()<=0)break;
	}
	if((int)s.size()>0)return false;
	return true;
}
void solve(){
	cin>>n;
	for(int i=1;i<=n;i++)cin>>a[i]>>w[i];
	int l=0,r=1e18;
	while(l<r){
		int mid=l+r+1>>1;
		if(ch(mid))
			l=mid;
		else
			r=mid-1;
	}
	cout<<l<<'\n';
}
signed main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0),cout.tie(0);
	int t=1;
	cin>>t;
	while(t--)
		solve();
}