s=raw_input("")
prop=s.split(" ")
k=int(prop[0])
m=int(prop[1])
n=int(prop[2])
if (n==1) and (m==1) and (k==1):
    print "0"
elif ((n!=1) and (m!=1)) or ((n==1) and (m==1) and (k<=3)):
    print "Impossible"
elif (n==1) and (m==1):
    print str(k-1)
    for i in range(2,k):
        print "1 " + str(i)
    print "2 " + str(k)
elif (m==1):
    print str(k-n)
    for i in range(2,k-n+2):
        print "1 " + str(i)
elif (n==1):
    print str(k*(m-1)-m*(m-1)/2)
    for i in range(1,m):
        for j in range(i+1,k+1):
            print str(i) + " " + str(j)