#include <iostream>
#include <fstream>
#include <string>

using namespace std;

string prim;

void ciur(int N)
{
	int i, j, rez = 1;
	
	prim.resize(N);

	for(i=3;i<=N;i+=2)
		if(!prim[i])
		{
			++rez;
			
			for(j=i+i+i;j<=N;j+=i)		
				prim[j] = 1;
		
		}
	
	cout<<rez<<"\n";
}

int main()
{

	int N;
	
	freopen("ciur.in", "r", stdin);
 	freopen("ciur.out", "w", stdout);
	
	cin>>N;
	
	fclose(stdin);
	
	ciur(N);
	
	fclose(stdout);

}