#include<stdio.h>

int eratosthenes(int n) {
	char *a = malloc(2000005 * sizeof(char));
	int count = 0;
	for (int i = 2; i <= n; i++)
		a[i] = 1;
	for (int i = 2; i <= n; i++)
		if (a[i] == 1)
		{
			count++;
			for (int j = i + i; j <= n; j += i)
				a[j] = 0;
		}
	free(a);
	return count;
}

int main()
{
	int n;
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	scanf("%d", &n);
	printf("%d", eratosthenes(n));
	return 0;
}