#include <iostream>
#include <fstream>
#include <math.h>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

bool prim[2000005];

int main()
{
    int i, j, N, cnt = 0;
    in >> N;

    for (i = 2; i <= N; i++)
        if (!prim[i])
        {
            ++cnt;
            for (j = i * i; j <= N; j += i)
                prim[j] = true;
        }

    out << cnt << endl;
    in.close();
    out.close();
    return 0;
}