I=input
J=int
P=print
N=J(I())
T=I().split()
A={}
s=0
for i in range(N):
	a=J(T[i])
	A[i+1]=a
	s^=a
t=min(s,1)
P(t)
while len(A)!=0:
	if t==0:
		T=I().split()
		i=J(T[0])
		k=J(T[1])
		s=A[i]
		if s==k:del(A[i])
		else:
			A[i]-=k
			s^=s-k
	else:
		m=0
		L=list(A)
		for i in L:
			a=A[i]
			d=a-(a^s)
			if d==a:
				P(i,a)
				del(A[i])
				m=-1
				break;
			if m<d:
				m=d
				j=i
		if m!=-1:
			print(j,m)
			A[j]=A[j]^s
	r=J(I())
	if r==-1:exit(0)
	t=1-t