#include <cstdio>
int i,j,n,nr;
bool prim[2000005];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d\n",&n);
	
	prim[1]=true;
	nr=0;
	
	for (i=2;i<=n;i++) {
	if (prim[i]==false)
		{
		j=2;
		while(i*j<=n) 
			{
			prim[i*j]=true;
			j++;
			}
			nr++;
		}
	}
	printf("%d\n",nr);
	fclose(stdin);
	fclose(stdout);
	return 0;
}