#include<fstream>
using namespace std;

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

#define NMAX 2000001

bool Prim[NMAX];
int N,Count;

void Read(){
    f>>N;
}

void Solve(){
    for (int i = 1; i <= N; i++) {
        Prim[i] = true;
    }
    for (int i = 2; i <= N; i++) {
        if (Prim[i] == true) {
            Count++;
            for (int j = i + i; j <= N; j+= i) {
                Prim[j] = false;
            }
        }
    }
}

void Write(){
    g<<Count;
}

int main(){
    Read();
    Solve();
    Write();
}