#include <bits/stdc++.h>

using namespace std;

int n, cnt;

char prim[2000005];

int main(void)

{

    int i, j;



    ifstream in("ciur.in");

    ofstream out("ciur.out");



    in>>n;

    for (i = 2; i <= n; ++i)

        prim[i] = 1;

    for (i = 2; i <= n; ++i)

        if (prim[i])

        {

            ++cnt;

            for (j = i+i; j <= n; j += i)

                prim[j] = 0;

        }



    out<<cnt;



    return 0;

}