n = int(input())
ls = [i for i in range(n+1)]
for i in range(2, n+1):
  if ls[i] != i:
    continue
  for j in range(i, n+1, i):
    ls[j] -= ls[j] // i
ans = 0
for i in range(1, n+1):
  ans += ((n // i) - 1) * (ls[i] - 1)
print(ans)