#include<cstdio>
#include<cmath>
int prim[2000000],cnt,i,j,q,cont,n;
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(i=2;i<=n;i++)
		prim[i]=1;
	cnt=0;
	for(i=2;i<=n;i++)
		{
			++cnt;
			if(prim[i])
			{
				for(j=i*i;j<=n;j+=i)
					prim[j]=0;
			}
		}
	printf("%d",cnt);
	/*--cnt;
	cont=0;
	for(i=1;i<=cnt;i++)
		{
			q=sqrt(sum[i]);
			if(q*q==sum[i])
				++cont;
			if(cont==n)
				{
					printf("%d",sum[i]);
					i=cnt+1;
				}
		}
	return 0;
	*/
}