#include <bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
#include<ext/pb_ds/hash_policy.hpp>
#include<ext/pb_ds/trie_policy.hpp>
#include<ext/pb_ds/priority_queue.hpp>
#define int long long
const int MAXN=2e5+5;
struct node{
	int v,w;
}a[MAXN];
bool pd(int w,int n){
	std::priority_queue<int> p,q;
	for(int i=1;i<=n;i++){
		if(w>a[i].v)p.push(a[i].w);
		else q.push(a[i].v-w+a[i].w);
	}
	while(1){
		if(p.empty()||q.empty()){
			return p.empty();
		}
		if(p.top()>q.top())return 0;
		p.pop();
		q.pop();
	}
}
void solve(){
	int n;
    std::cin>>n;
	int maxx=0;
	for(int i=1;i<=n;i++){
		std::cin>>a[i].v>>a[i].w;
		maxx=std::max(maxx,a[i].v);
	}
	int l=1,r=maxx,ans=0;
	while(l<=r){
		int mid=(l+r)/2;
		if(pd(mid,n)){
        //std::cout<<mid<<'\n';
			ans=mid;
			l=mid+1;
		}
		else r=mid-1;
	}
    std::cout<<ans<<'\n';
}
signed main(){
	int t;
	std::cin>>t;
	while(t--)solve();
	return 0;
}