#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n, nr;
bool p[2000005];
int main()
{
    fin>>n;
    fin.close();
    int i,j;
    i=2;
    do
    {
        if ( p[i] == 0)
            for (j = i*i ; j <= n ; j = j + i)
                p[j] = 1;
        i++;
    }
    while (i <= n);
    nr = 0;
    for (i = 2; i <= n; i++)
        if (p[i] == 0)
            nr++;
    fout<<nr<<'\n';
    fout.close();
    return 0;
}