#include <iostream>
#include <fstream>
using namespace std;
int x;
char v[2000010];
ifstream f ("ciur.in");
ofstream g ("ciur.out");
int n;
void ciur ()
{
    int i, j;
    n=1;
    v[1]=1;
    for (i=3; i<=x; i+=2)
    {
        v[i+1]=1;
        if (v[i]==0)
        {
            for (j=i+i; j<=x; j+=i)
                v[j]=1;
            n++;
        }
    }
}
int main ()
{
    f>>x;
    ciur ();
    g<<n;
    return 0;
}