Codeforces Round #602 (Div. 2, based on Technocup 2020 Elimination Round 3) A Math Problem

//只要从所有区间右端点的最小值覆盖到所有区间左端点的最大值即可
#include<iostream>
using namespace std ;
int x,y;
int n;
int t;
int main() {
    cin>>t;
    while(t--) {
        cin>>n;
        if(n==) {
            cin>>x>>y;
            cout<<<<endl;
        } else {
            int l=,r=1e9+;
            for(int i=; i<=n; i++) {
                cin>>x>>y;
                l=max(l,x);
                r=min(r,y);
            }
            int ans=max(,l-r);
            cout<<ans<<endl;
        }
    }
    return ;
}