#include <bits/stdc++.h>

using namespace std;

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

const int Nmax = 2e6+5;
int k, Prime[Nmax];
bool viz[Nmax];

void ciur(int n){
    k=1;// nr 2
    for(int i = 3; i <= n; i= i+2)
        {
            if(viz[i] == 0){
                k++;
                for(int j = 2 * i; j <= n; j = j + i){
                    viz[j] = 1;
                }
            }
        }
    }
int main()
{
    int n;
    in>>n;
    ciur(n);
    out<<k;
    return 0;
}