#include <iostream>
#include <fstream>

using namespace std;

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

int n, s, i, j;
bool v[2000001];

int main()
{
    fin >> n;
    for(i = 2; i <= n; i++)
    {
        if (v[i] == 0)
        {
            k++;
            for (j = i + i; j <= n; j += i)
            {
                v[j] = 1;
            }
        }
    }
    fout << k;
    return 0;
}