from functools import cmp_to_key

def f(r1, r2):
    x1, y1,_ = r1
    x2, y2,_ = r2
    if  x2 * y1 - y2 * x1==0:
        return x1-x2
    else:
        return x2 * y1 - y2 * x1




N = int(input())
XY = [list(map(int, input().split())) for _ in range(N)]
XYI = []
for i,(x,y) in enumerate(XY):
    XYI.append([x,y,i+1])

XYI.sort(key = cmp_to_key(f))
print(N//2)
for i in range(N//2):
    print(XYI[i*2][2],XYI[i*2+1][2])