EDGE=[]

for i in range(1,1003):
    EDGE.append((i,i+1))

now=1004
for j in range(4):
    EDGE.append((1,now))
    now+=1

for i in range(2,1003):
    for j in range(6):
        EDGE.append((i,now))
        EDGE.append((now,now+1))
        now+=2

print(len(EDGE)+1)
for x,y in EDGE:
    print(x,y)