#include <bits/stdc++.h>

//DEBUG:    https://github.com/sharkdp/dbg-macro
#ifdef LOCAL
#include "../dbg-macro-0.5.1/dbg.h"
#else
#define dbg(...) (__VA_ARGS__)
#endif

#define endl '\n'
using namespace std;
typedef long long ll;
const ll MAXN=2e5+10,MOD=1e9+7,INF=1e9;

ll qpow(ll base,ll exp){ll ans=1;while(exp){if(exp&1)(ans*=base)%=MOD;(base*=base)%=MOD;exp>>=1;}return ans;}
template<class T>ll max_binary_answer(ll l,ll r,T check,bool cmp=true){ll m;while(l<r){m=(l+r+1)/2;if(cmp^!check(m))l=m;else r=m-1;}return l;}
template<class T>ll min_binary_answer(ll l,ll r,T check,bool cmp=true){ll m;while(l<r){m=(l+r)/2;if(cmp^!check(m))r=m;else l=m+1;}return r;}
ll exgcd(ll a,ll b,ll &x,ll &y){ll tmp;return b==0?(x=1,y=0,a):(tmp=exgcd(b,a%b,y,x),y-=(a/b)*x,tmp);}
ll highbit(ll x){for(ll i=1;i<(ll)sizeof(ll)*4;i<<=1)x|=x>>i;return x-(x>>1);}
ll lowbit(ll x){return x&(-x);}
//--------Global declared area--------

//--------Global declared end --------
void solve(int test_num){
	int n;
	cin>>n;
	vector<pair<ll,ll>> a(n+1);
	for(int i=1;i<=n;i++){
		int v,w;
		cin>>v>>w;
		a[i]={v,w};
	}
	sort(a.begin()+1,a.end(),[&](pair<ll,ll>x,pair<ll,ll>y){
		if(x.first+x.second==y.second+y.first)
		{
			if(x.first!=y.first)
				return x.first<y.first;
			else return x.second<y.second;
		}
		return x.first+x.second<y.first+y.second;
	});
//	for(int i=1;i<=n;i++){
//		cout<<a[i].first<<' '<<a[i].second<<'\n';
//	}
	ll ans=1e9;
	if(n==1){
		cout<<a[n].first;
		return;
	}else{
		if(a[n].second>a[n-1].second){
			//cout<<12345;
			ans=min(ans,a[n].first);
		}else {
			//cout<<a[n-1].second-a[n].second<<' ';
			ans=min(ans,a[n].first-(a[n-1].second-a[n].second));
		}
	}
	cout<<ans<<'\n';
	return;
}
/*
	5 
	1 5
	2 4
	3 3
	5 1
	4 2
*/
int main(){
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr),std::cout.tie(nullptr);
	int t=1;
	cin>>t;
	for(int i=1;i<=t;i++){
		solve(i);
	}
	return 0;
}