codeforces 1334C（前缀和）

#include<bits/stdc++.h>
#define x first
#define y second
#define PB push_back
#define mst(x,a) memset(x,a,sizeof(x))
#define all(a) begin(a),end(a)
#define rep(x,l,u) for(ll x=l;x<u;x++)
#define rrep(x,l,u) for(ll x=l;x>=u;x--)
#define sz(x) x.size()
#define IOS ios::sync_with_stdio(false);cin.tie(0);
using namespace std;
typedef unsigned long long ull;
typedef pair<int,int> PII;
typedef pair<char,char> PCC;
typedef long long ll;
typedef pair<ll,ll> PLL;
const int N=3*1e5+10;
const int M=1e6+10;
const int INF=0x3f3f3f3f;
const int MOD=1e9+7;
/*
独立思考
不要看测试样例
找性质
试着证明
写完后不盲目交
*/
ll a[N*2],b[N*2],f[N*2];
void solve(){
    int n;scanf("%lld",&n);
    ll ans=0;
    rep(i,1,n+1){
        scanf("%lld%lld",&a[i],&b[i]);
        ans+=a[i];
        a[i+n]=a[i];
        b[i+n]=b[i];
    }
    f[1]=0;
    rep(i,2,n*2+1){
        if(a[i]-b[i-1]>0) f[i]=f[i-1]+a[i]-b[i-1];
        else f[i]=f[i-1];
    }
    rep(i,n,n*2+1){
        ans=min(ans,f[i]-f[i-n+1]+a[i-n+1]);
    }
    cout<<ans<<endl;
}
int main(){
    //IOS;
    //freopen("test.txt", "r", stdin);
    //freopen("test.txt", "w", stdout);
    int t;cin>>t;
    while(t--)
        solve();
    return 0;
}