#include <iostream>
#include <fstream>

using namespace std;

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

bool v[2000001];

int main()
{
    int N, ct = 1 , i , j;
    fin >> N;
    for(i = 4 ; i <= N ; i += 2)
        v[i] = 1;
    for(i = 3 ; i <= N ; i += 2)
    {
        if(v[i] == 0)
        {
            ct++;
            for(j = i ; j <= N / i; j++)
                v[j * i] = 1;
        }
    }
    fout << ct;


    return 0;
}