//#include <iostream>
#include <fstream>
using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");
int x[20000004];

int main()
{
    int n, cont = 0;
    cin >> n;
    for(int i = 2; i <= n / 2; i++)
    {
        if(x[i] == 0){
            cont++;
            for(int j = i + i; j <= n; j += i)
                x[j] = 1;
        }
    }
    cout << cont;
    return 0;

}