import math

n = int(input())

list_num = list(range(1, n + 1))
list_num[0] = 0

for i in range(2, int(math.sqrt(n)) + 1):
    if list_num[i - 1] == 0:
        continue
    
    multiple = 2
    while True:
        target = i * multiple
        if target > n:
            break
        list_num[i * multiple - 1] = 0
        multiple += 1
        
print(sum(list_num))