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


int N;


// The Seive of Eratosthenes
int Sieve(int N)
{
	int result = N - 1;
	int square_root = (int) sqrt((double)N);
	
	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 <= square_root; ++i)
		for (int j = i + i; j <= N; j += i)
			if (primes[j])
			{
				primes[j] = 0;
				--result;
			}

	return result;
}

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

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

	return 0;
}