def Bisect_Int(ok,ng,is_ok):
    while abs(ok-ng)>1:
        mid=(ok+ng)//2
        if is_ok(mid):
            ok=mid
        else:
            ng=mid
    return ok

T=int(input())
for t in range(T):
    N=int(input())
    V,W=[],[]
    for i in range(N):
        v,w=map(int,input().split())
        V.append(v)
        W.append(w)
    def is_ok(ans):
        A,B=[],[]
        for v,w in zip(V,W):
            if ans<v:
                A.append(v+w-ans)
            elif v<ans:
                B.append(w)
        A.sort(reverse=True)
        B.sort(reverse=True)
        if len(A)<len(B):
            return False
        for a,b in zip(A,B):
            if a<b:
                return False
        return True
    ans=Bisect_Int(0,1<<40,is_ok)
    print(ans)