#include<fstream>
#include<malloc.h>
using namespace std;
 
ifstream f("ciur.in");
ofstream g("ciur.out");
 
#define NMAX 20000000
 
int n = 0,nr = 0;
short a[NMAX];
 
void eratosthenes()
{
    for(int i = 2; i <= n; i+=2)
        a[i] = 1;
     
    for(int i = 3; i <= n; i += 2)
    {
        if(!a[i])
        {
            for(int j = i + i + i; j <= n; j += i + i )
                a[j] = 1;
        }
    }
}
 
int main()
{
    f>>n;
     
    eratosthenes();
     
    for(int i = 2; i <= n; ++i)
        if(a[i] == 0)
            nr++;
     
    g<<nr;
     
    g.close();
     
    return 0;
}