#include<iostream>
#include<cstdio>
using namespace std;
bool c[2000010];

int n;

void ciur()
{

	int i;

	c[0]=1;

	c[1]=1;

	for(i=4;i<=n;i+=2)
	
		c[i]=1;

	for(i=3;i*i<=n;i+=2)
	
		if(c[i]==0)
		
			for(int j=i*i;j<=n;j=j+2*i)
			
				c[j]=1;
}
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	int i,nr=0;
	
	cin>>n;
	
	ciur();
	
	for(i=2;i<=n;i++)
		
		if(c[i]==0)
			
			nr++;
	
		cout<<nr;	
	
		return 0;
}