#include <iostream>
#include <fstream>
#include <bitset>

using namespace std;

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

bitset < 2000001 > c;//false egal prim

int ciur(int n)
{
    int i, j, nr = 1;
    for(i = 4; i <= n; i += 2)
        c[i] = true;
    for(i = 3; i <= n; i += 2)
    {
        if(!c[i])
        {
            ++nr;
            for(j = 2 * i; j <= n; j += i)
                c[j] = true;
        }
    }
    return nr;
}

int main()
{
    int n;
    fin>>n;
    fout<<ciur(n);
    return 0;
}