data_map = [[0] + [1]*1001 + [0]*3000, [0]*4002, [0]*4002, [0]*4002]
for i in range(1,4):
  for j in range(1,4002):
    k = 0 if j < 1000 else j-1000
    data_map[i][j] = sum(data_map[i-1][k:j+1])

while True:
  try:
    line = int(raw_input())
  except:
    break
  print data_map[3][line+1]