code:

#include<bits/stdc++.h>
using namespace std;
int t,n,a[300005],b[300005],sum,mini;
int main(){
	cin>>t;
	while(t--){
		sum=0;
		mini=1e9;
		cin>>n;
		for(int i=1;i<=n;i++) cin>>a[i]>>b[i];
		for(int i=1;i<=n;i++) sum+=max(0,a[i]-b[i>1?i-1:n]),mini=min(mini,a[i]);
		cout<<sum+mini<<endl;
	}
	return 0;
}