#include<fstream>
#define max 2000100
using namespace std;

ifstream f ("ciur.in");
ofstream g ("ciur.out");

int n,i,j,contor;
bool v[max];

int main(){
	f>>n;
	for (i=2; i<=n; i++)
if(!v[i])
{contor ++;
for(j=i; j<=n; j+= i)
v[j] = true;}
g<<contor;
return 0;
}