#include <iostream>
#include <fstream>
#define nmax 2000000
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,Numar;
bool prim[nmax];
void citire() {
    f>>n;
}
void Ciur() {
    prim[1]=1;
    for (int i=2;i<=n;i++) {
        if (prim[i]==0) {
            Numar++;
            for (int j=i+i;j<=n;j=j+i) {
                prim[j]=1;
            }
        }
    }
}
void rez() {
    Ciur();
    g<<Numar;
}
int main() {
    citire();
    rez();
    return 0;
}