#include <iostream>
#include <fstream>

using namespace std;

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

int main()
{
    int v[200001], N, ct = 0 , i , j;
    fin >> N;
    for(i = 1 ; i <= N; i++)
        v[i] = 1;
    for(i = 2 ; i <= N ; i++)
    {
        if(v[i] == 1)
        {
            ct++;
            for(j = i+i ; j <= N ; j = j + i)
                v[j] = 0;
        }
    }
    fout << ct;


    return 0;
}