#include <bits/stdc++.h>

using namespace std;

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

int n, sol;
bitset <2000005> prim;

void Ciur()
{
    int i, j;
    prim[1] = prim[0] = 1;
    for (i = 4; i <= n; i += 2)
        prim[i] = 1;

    for (i = 3; i * i <= n; i += 2)
        if (prim[i] == 0)
        for (j = i * i; j <= n; j += 2 * i)
            prim[j] = 1;

    for (i = 2; i <= n; i++)
        sol += (prim[i] == 0);
}

int main()
{
    fin >> n;
    Ciur();
    fout << sol << "\n";

    return 0;
}