n=int(input())
p=[[] for i in range(n+1)]
for i in range(2,n+1):
  if len(p[i])==0:
    for j in range(i,n+1,i):
      p[j]+=[i]
a=n*(n-1)//2
for i in range(2,n+1):
  u=i
  f=1
  for v in p[i]:
    f*=v-1
    u//=v
  f*=u
  a-=f
  a-=n//i-1
print(a)