#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;

using i64 = long long;
using u64 = unsigned long long;
#define Z cout << "\n"
#define lb lower_bound
#define ub upper_bound
#define inf 0x3f3f3f3f
#define INF 0x3f3f3f3f3f3f3f3f
#define unq(x) sort(x.begin(), x.end()), x.erase(unique(x.begin(), x.end()), x.end())
#define D(x) cerr << #x << ": " << (x) << "\n"
#define DV(v) cerr<< #v << ": "; for(int i=0;i <(v).size(); i++)cerr << ((v)[i]) << ",";cerr << "\n"
#if 0
#define int i64
#endif

struct node {
    int v, w, no;
    bool operator <(const node& o)const {
        return v + w <= o.v + o.w;
    }
    bool operator >(const node& o)const {
        return v + w > o.v + o.w;
    }
};

void solve() {
    int n;
    cin >> n;

    vector<node>a(n + 1);
    set<node, greater<node>>se;
    set<pair<int, int>>S;
    for (int i = 1; i <= n; i++) {
        cin >> a[i].v >> a[i].w;
        a[i].no = i;
        se.insert(a[i]);
        S.insert({ a[i].v,i });
    }

    while (1) {
        auto B = *S.begin();
        auto top = *se.begin();
        int yv = top.v;
        int v = top.w + top.v - a[B.second].w;
        v = min(v, yv);
        //D(v);
        se.erase(se.begin());
        if (v < 0)break;
        se.insert({ v,top.w,top.no });
        se.erase({ B.first,a[B.second].w,B.second });
        S.erase(S.begin());
        S.erase({ top.v,top.no });
        S.insert({ v, top.no });
    }
    cout << S.begin()->first << "\n";
}

signed main() {
    cin.tie(0)->sync_with_stdio(false);
    int t;
    cin >> t;
    while (t--)solve();
    return 0;
}