#include<stdio.h>
const int N=2000005;
int n,i,j,prim,nr=0;
bool c[N];

int main()

{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
//	for(i=1;i<=N;i++)
//		c[i]=false;
	for(i=2;i*i<=n;i++)
	{
		if (c[i]==false)
		{
			for(j=i*i;j<=n;j=j+i)
			c[j]=true;
		}
	}
	for(i=2;i<=n;i++)
	{
		if(!c[i]) 
			nr=nr+1;
	}
	printf("%d",nr);
}