#include<fstream.h>

long i, j, n, c, nr, d, ok;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
	fin>>n;
	
	for(i=2;i<=n;i++)
	{
		ok = 1;
		d = 2;
		while((d<=i/2)&&(ok==1))
		{
			if(i%d==0)
				ok = 0;
			
			d++;
		}
		
		if(ok == 1)
			c++;
	}
	
	fout<<c;
	
	fout.close();
	
	return 0;
}