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

int N, i, j, k;
bool div[1000000];

int main()
{
    ifstream fin("ciur.in");
    fin >> N;
    fin.close();
    
    k = 1; // N >= 2

    for(i = 3; i<=N; i+=2)
    {
        if(div[(i-1)/2] == false)
        {
            ++k;
        
            for(j = i+i+i; j<=N; j += i+i)
                div[(j-1)/2] = true;
        }
    }
    
    ofstream fout("ciur.out");
    fout << k;
    fout.close();
    
    return 0;
}