#include <iostream>
#include<fstream>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <bitset>
#include <climits>

using namespace std;

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

bitset <2000010> p;

int eratostene(int n)
{
    int k = 0;
    p[0] = p[1] = 1;
    for (int i = 2; i <= n; i++)
    {
        if (p[i] == 0)
        {
            k++;
            for (int j = 2*i; j <= n; j += i)
                p[j] = 1;
        }
    }
    return k;
}


int main()
{
    int n;
    fin >> n;
    fout << eratostene(n);
}