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