#include<iostream>
#include<fstream>
#include<math.h>
using namespace std;
int prim(int n)
{
int ok=1,i;
for (i=2;i<=sqrt(n);i++)
if (n%i==0)
{ok=0;break; }
else
ok=1;

return ok;
}

int main ()
{int contor=0,i,n;

    ifstream f("ciur.in");
	ofstream g("ciur.out");
	
f>>n;
	for(i=2;i<=n;i++)
	{
		if(prim(i)==1 )
			//if (ok==1)
			contor ++;
	}
	g<<contor;
	//g<<prim(7)<<" "<<prim(6);

return 0;
}