#include <fstream>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

int v[2000010];
int n;
int nr;


int main()
{
    in >> n;

    for(int i=2; i<=n; i++)
    {
        if(v[i] == 0)
        {
            nr++;
            for(int k=i; k<=n; k+=i)
                v[i] = 1;
        }
    }



    return 0;
}