I,R=input,range
J=lambda:map(int,I().split())
for t in R(int(I())):
	N,L,K=J()
	A=sorted(list(J()))
	A=[i//N*L+A[i%N]for i in R(N*3)]
	p,P=-1,L
	while p+1<P:
		m,l,r,b=(p+P)>>1,-P,0,1
		for i in R(N+1):
			x,y=A[i+K-1]-m,A[i]+m+1
			if x<y:
				if l+P:b&=x<r
				else:l=x
				r=y
		if (l+L<r)*b:P=m
		else:p=m
	print(P)