#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>

int main(void)
{
	int n, vector[2000005];
	int contor = 0;

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

	scanf("%d", &n);
	int i, j;
	for (i = 2; i <= n; i++)
	{
		vector[i] = 1;
	}
	for (i = 2; i <= n; i++)
	{
		if (vector[i])
		{
			contor++;
			for (j = i + i; j <= n; j = j + i)
			{
				vector[j] = 0;
			}
		}
	}
	printf("%d", contor);
}