#include <bits/stdc++.h>
using namespace std;

#define IN "ciur.in"
#define OUT "ciur.out"

int main()
{
    ifstream fin(IN);
    ofstream fout(OUT);
    int N;

    fin>>N; //am citit numarul
    int A[N+1]; //am intializat vecto

    for(int i=2;i<=N;i++) A[i]=0; //bag toate numerele de la 0pana la n inclusiv in ciur

    for(int i=2;i<=N;i++)
    {
        int p=2;
        while(i*p<=N)
        {
            A[i*p] = 1;
            p++;
        }
    }
    int nr =0;
    for(int i=2;i<=N;i++)
        if(A[i] == 0) nr++;
    fout<<nr;
    return 0;
}