#ifdef WIN32
#define _CRT_SECURE_NO_WARNINGS
#endif

#include <stdio.h>

char prim[2000896];


int main()
{
	freopen("ciur.in", "rt", stdin);
	freopen("ciur.out", "wt", stdout);

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

	int sol = 0;
	for (int i = 2; i <= n; i++)
		if (prim[i] == 0)
			sol++;

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

	return 0;
}