#include <iostream>
#include <fstream>

using namespace std;

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

int N,k;
bool a[2000002];

int main()
{
    fin >> N;
    k = 1;

    for(int i = 4; i <= N; i += 2){
        a[i] = 1;
    }
    for(int i = 3; i <= N; i += 2){
        if(a[i] == 0){
            k++;
        for(int j = i + i; j <= N; j += i){
            a[j] = 1;
         }
        }
    }
    fout << k;
    return 0;
}