#include <iostream>
#include <fstream>
using namespace std;

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

const int NMAX = 2000000;
int N, v[1 + NMAX], nr;
int main()
{
    fin >> N;
    for(int i = 2; i <= N; i++)
    {
        if(v[i] == 0)
        {
            nr ++;
            for(int j = 2 * i; j <= N; j += i)
                v[j] = 1;
        }
    }
    fou << nr;
}