//*CODE BY SERBAN ANDREI*


#include <bits/stdc++.h>


#define nmax 2000007

using namespace std;

bool v[nmax];

unsigned long i,n,j,cont=0;

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");

    f>>n;

    for(i=2;i<=n;++i)
    {

        if(!v[i])
        {

            cont++;
            for(j=2*i;j<=n;j+=i)
                v[j]=1;
        }

    }

    g<<cont;
    g.close();

    return 0;
}