#include <stdio.h>
#include <stdlib.h>

int N;


// The Seive of Eratosthenes
int Sieve(int N)
{
	int half = N / 2;
	int result = 0;
	char* primes = (char*) calloc(sizeof(char), N + 1);
	if (primes == NULL) exit(1);

	for (int i = 2; i <= N; ++i) 
		primes[i] = 1;

	for (int i = 2; i <= half; ++i)
		for (int j = i + i; j <= N; j += i)
			primes[j] = 0;

	for (int i = 2; i <= N; ++i)
		if (primes[i]) ++result;

	return result;
}

void main(void) 
{
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);

	scanf("%d", &N);
	printf("%d\n", Sieve(N));
}