#include    <iostream>
#include    <fstream>
#include    <cmath>

using namespace std;

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

const int NMAX = 2000005;

bool A[NMAX];
int n, cnt;



int main() {
    fin >> n;
    for(int i = 2; i <= n; ++i) A[i] = true;
    for(int i = 2; i <= n; ++i){
        if(A[i] == true){
            ++cnt;
            for(int j = i+i; j <= n; j+=i){
                A[j] = false;
            }
        }
    }
    fout << cnt;
    fout.close();
    fin.close();
    return 0;
}