#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>

int n;
char vector[2000005];
int contor = 0;

int main(void)
{
	if (freopen("ciur.in", "r", stdin) != NULL)
	{
		if (freopen("ciur.out", "w", stdout) != NULL)
		{
			if (scanf("%d", &n) != 0)
			{
				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);
			}
		}
	}
}