#include <cstdio>

using namespace std;

bool ciur[2000010];
int n;
int numerePrime;

void citire(){
    scanf ("%d", &n);
}

void Ciur (){
    for (int i = 2; i <= n; ++ i){
        if (ciur[i] == 0){
            numerePrime ++;
            for (int j = i + i; j <= n; j += i){
                ciur[j] = 1;
            }
        }
    }
}

void afisare(){
    printf ("%d", numerePrime);
}

int main()
{
    freopen ("ciur.in", "r", stdin);
    freopen ("ciur.out", "w", stdout);

    citire();
    Ciur();
    afisare();

    return 0;
}