#include <stdio.h>

int n, contor;
char nr_prime[2000005];

int main()
{
	int i, j;
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
    scanf("%d", &n);

	for (i = 2; i <= n; ++i)
			nr_prime[i] = 1;

	for (i = 2; i <= n; ++i)
		if (nr_prime[i])
		{
			++contor;
			for (j = 2*i; j <= n; j = j+i)
				nr_prime[j] = 0;
		}

	printf("%d\n", contor);

	return 0;
}