#include <iostream>
#include <bitset>
#include <cmath>
#include <fstream>
using namespace std;

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

const int MAX =  2000005;

bitset<MAX>p;

int nrP = 1;

int main()
{
    int i, j, n;

    fin>>n;

    p[0] = p[1] = 1;

    int r = sqrt(n);

    for(i=3; i<=r; i+=2)
    {
        if(!p[i])
        {
            nrP++;
            for(j=i*i; j<=n; j+=(2*i))
            {
                p[j] = 1;
            }
        }
    }

    if(!p[r])
    {
        r+=2;
    }
    r += (r%2 == 0);

    for(i=r; i<=n; i+=2)
    {
        if(!p[i])
        {
            nrP++;
        }
    }
    fout<<nrP;
    fin.close();
    fout.close();
    return 0;
}