#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n,nr;
bool b[2000005];
int main()
{
    in>>n;
    for(int i=3;i<=n;i+=2)
    {
        if(!b[i])
        {
            nr++;
            for(int j=i*3;j<=n;j+=2*i)
            {
                b[j]=1;
            }
        }
    }
    return 0;
}