#include <iostream>
#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

const int NMAX = 2000000;

int prim[NMAX];
int n;

int main()
{
    fin >> n;
    int cnt = 0;

    for(int i = 2; i <= n; i++)
        prim[i] = 1;

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

    fout << cnt;
    return 0;
}