#include<iostream>
#include<math.h>
#include<stdio.h>
using namespace std;

char v[2000001];

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

	int p = sqrt((double)n);
	for(i=2;i<= p;i++)
	{ 
		if(v[i]==1) 
			for(j=i*i;j<=n;j+=i)
		       v[j]=0;
	  
	}


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

cout<<c;
return 0;


}