#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
int n;
bool a[2000005];
void ciur(int c)
{
    for(int i=3;i*i<=c;i+=2)
    {
        if(a[i]==false){
            for(int j=i*i;j<=c;j+=2*i)
                a[j]=true;
        }
    }
    int k=1;
    for(int i=3;i<=c;i+=2)
        if(a[i]==false)
            k++;
    out<<k<<'\n';

}
int main()
{
    in>>n;
    ciur(n);
    return 0;
}