#include<iostream>
#include<fstream>
#define FIN "ciur.in"
#define FOUT "ciur.out"
#define MAXN 2000000
using namespace std;

ifstream f(FIN);
ofstream g(FOUT);

bool prim[MAXN];

int main()
{
    int n;
    f >> n;

    int counter = 0;
    for(int i=2; i<=n; i++)
    {
        if(prim[i] == 0)
            counter++;

        for(int j=i; j<=n; j+=i)
            prim[j] = 1;
    }

    g << counter;

    return 0;

}