// ciurul lui eratostene.cpp : Defines the entry point for the console application.
//


using namespace std;
#include<fstream>
int long n,prim[20000004];
ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{
	f>>n;
long int i,j,index=0;
for(i=2;i<=n;i++)
 prim[i]=1;
for(i=2;i<=n;i++)
{ 
	if(prim[i]==1)
	{
		index++;
		for(j=i+i;j<=n;j+=i)
			{ 
			  prim[j]=0;

			}
	}
}

g<<index;
	return 0;
}