#include <fstream>
#include<iostream>

using namespace std;

int N, d;
char prim[2000000];

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

    int i,j;

    f >> N;

    for (i = 2; i <= N; i++)
        prim[i] = 1;
    for (i = 2; i <= N; i++)
    {
        if(prim[i])
        {
            d++;
            for (j = i+i; j <= N; j += i)
                prim[j] = 0;
        }

    }
    g << d << endl;
    g.close();
    return 0;
}