#include <iostream>
#include <fstream>

using namespace std;

int n;
bool  a[2000003];
long long nr;

int main () {

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

    f >> n;

    int i, j;
    for ( i = 2; i * i <= n; ++i ) {
        if ( a[i] == false ) {
            for ( j = i * i; j <= n; j += i ) {
                a[j] = true;
            }
        }
    }

    for ( i = 2; i <= n; ++i ) {
        if ( a[i] == false ) {
            nr++;
        }
    }

    g << nr;

    return 0;
}