n=int(input())
ans=0
maxsqrt=0
a=[1]*(n+1)
a[0]=0
i=2
while i*i<=n:
  j=i*i
  for k in range(j,n+1,j):
    a[k]=0
  i+=1
sums=[0]*(n+1)

currsum=0
for i in range(n+1):
  currsum+=a[i]
  sums[i]=currsum
while (maxsqrt+1)*(maxsqrt+1)<=n:
  maxsqrt+=1
b=1

while b*b<=n:
  ans+=(2*b-1)*(sums[n//(b*b)])
  b+=1
print(ans)