#include<iostream.h>
#include<fstream.h>
#include<vector>
using namespace std;

vector <bool> a(2000000);
int main()
{ifstream f("ciur.in");
ofstream h("ciur.out");
int n,i,j,k=0;
f>>n;
for(i=2;i<=n;i++)
	if(a[i]==0)
		for(j=2;j<=n/i;j++)
			a[i*j]=1;
	for(i=2;i<=n;i++)
if(a[i]==0)
k++;
h<<k;
return 0;}