#include    <iostream>
#include    <fstream>

using namespace std;

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

const int NLIM = 2000005;
bool isPrime[NLIM];

int N, answer;
void Read()
{
    fin >> N;

    for(int i = 2; i <= N; i++)
        isPrime[i] = true;

    for(int i = 2; i <= N; i++)
    {
        if(isPrime[i])
        {
            answer += 1;
            for(int d = i + i; d <= N; d += i)
                isPrime[d] = false;
        }
    }

    fout << answer;
}

int main()
{
    Read();
    return 0;
}