MOD = 10 ** 9 + 7
INF = 10 ** 10
import sys
sys.setrecursionlimit(100000000)

def sieve(n):
    primes = [1 if i%2 == 1 else 0 for i in range(n + 1)]
    primes[1] = 0
    primes[2] = 1
    for i in range(3,n + 1,2):
        if i * i > n:
            break
        if primes[i]:
            for j in range(i * i,n + 1,i):
                primes[j] = 0
    return sum(p for p in range(2,n + 1) if primes[p] == 1)

def main():
    N = int(input())
    print(sieve(N))
if __name__ == '__main__':
    main()