def eratosthenes(n):
  if n < 2:
    return [0]
  if n == 2:
    return [2]
  prime = [2]
  limit = int(n**0.5)+1
  data = [i for i in range(3, n+1, 2)]
  while True:
    p = data[0]
    if limit <= p:
      return prime + data
    prime.append(p)
    data = [e for e in data if e%p!=0]

def main():
  n = int(input())
  arr = eratosthenes(n)
  print(sum(arr))

main()