n = int(input())
xy = sorted([tuple(map(int,input().split())) for _ in range(n)])
f = [False]*n
print(n//2)
for i,(ix,iy) in enumerate(xy):
    if f[i]: continue
    f[i] = True; md = 16001; mj = -1
    for j,(jx,jy) in enumerate(xy):
        d = abs(ix-jx)+abs(iy-jy)
        if not f[j] and d<md: md = d; mj = j
    f[mj] = True
    if mj!=-1: print(i+1,mj+1)