#include <fstream>
#include <iostream>

using namespace std;

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

int ciur[2000001], nr;

int main()
{
    nr = 2000000;
    ciur[0] = 1, ciur[1] = 1;

    for (int i = 2; i * i <= nr; i++)
        if (ciur[i] == 0)
            for (int j = 2; j <= nr / i; j++)
                ciur[i * j] = 1;

    int n, cnt = 0;

    fin >> n;

    for (int i = 1; i <= n; i++)
        if (ciur[i] == 0)
            cnt++;
    fout << cnt;
}