#include <iostream>
#include <fstream>

using namespace std;

bool pr[2000001];

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int prime,n;
    f>>n;
    prime = 0;
    for(int i = 2 ; i <= n ; ++i){
        if(pr[i] == 0){
            ++prime;
            for(int j = i + i ; j <= n ; j += i)
                pr[j]=1;
        }
    }
    g << prime;
    return 0;
}