#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
#define MAX_SIZE 2000000
int n, i, j, cate;
bool prim[MAX_SIZE];


void Ciur() {
    prim[0] = prim[1] = 1;
    for(i = 2; i <= n; i++)
        if(prim[i] == 0) {
            cate++;
            for(j = 2; i*j <= n; j++)
                prim[i*j] = 1;
        }

}

int main()
{
    f >> n;

    Ciur();

    g << cate;
    return 0;
}