#include <iostream>
#include <fstream>

using namespace std;

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

const int NMAX = 2000000 + 5;

int n, cnt;
bool prime[NMAX];

void ciur()
{
    prime[0] = prime[1] = 1;
    for (int i = 2; i <= n; ++i)
        if (!prime[i])
        {
            ++cnt;
            for (int j = i + i; j <= n; j += i)
                prime[j] = 1;
        }
}

int main()
{
    fin >> n;
    ciur();
    fout << cnt;

    return 0;
}