// ciurul lui Eratostene
#include <stdio.h>
//bool prim[2000100];
int prim[100000000];
int main()
{
	int n,i,j,nr=0;

	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	scanf("%d", &n);

	for (i=2;i<=n/2;i++)
	{
		if (!prim[i])
		{
			nr++;
			for (j=i*3+1;j<=n/2;j+=i*2+1)
				prim[j]=1;
		}
	}
	nr++;
	printf("%d\n",nr);	
	return 0;
}