n=int(input())
f=list(range(n+1))
a=n*(n-1)//2
for i in range(2,n+1):
  a-=n//i-1
  if f[i]==i:
    for j in range(i,n+1,i):
      f[j]*=i-1
      f[j]//=i
  a-=f[i]
print(a)