#include<bits/stdc++.h>
#define gt getchar
#define pt putchar
#define ll long long
#define ull unsigned long long
using namespace std;
const int MAXN=1e5+10;
struct node{
    int v;
    int w;
}a[MAXN];
bool cmp(node a,node b){
    if(a.v!=b.v)return a.v<b.v;
    else return a.w<b.w;
}
int n;
inline bool check(int x){
    priority_queue<int>p;
    priority_queue<int>q;
    for(int i=1;i<=n;i++){
        if(x>a[i].v) p.push(a[i].w);
        else q.push(a[i].v-x+a[i].w);
    }
    while(true){
        if(q.empty()||p.empty()){
            if(p.empty()) return true;
            else return false;
        }
        if(p.top()>q.top()) return false;
        q.pop();
        p.pop();
    }
}
void solve(){
    memset(a,0,sizeof(a));
    cin>>n;
    for(int i=1;i<=n;i++)
        cin>>a[i].v>>a[i].w;
    int l=1,r=1e9,ans=0;
    while(l<=r){
        int mid=(l+r)>>1;
        if(check(mid)){
            l=mid+1;
            ans=mid;
        }
        else r=mid-1;
    }
    cout<<ans<<'\n';
}
signed main(){
	ios::sync_with_stdio(0);
    int T;
    cin>>T;
    while(T--) solve();
    return 0;
}