#include <bits/stdc++.h>

using namespace std;

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

bitset<2000001>a;

void Ciur(int n)
{
    int i, j;
    a[0] = a[1] = 1;
    for (i = 4; i <= n; i += 2)
        a[i] = 1;
    for (i = 3; i * i <= n; i += 2)
    {
        if (a[i] == 0)
            for (j = i * i; j <= n; j += 2 * i)
                a[j] = 1;
    }
}

int main()
{
    int n, i, nr = 0;
    fin >> n;
    Ciur(n);
    for (i = 1; i <= n; i++)
        if(a[i] == 0)
            nr++;
    fout << nr << "\n";
    fout.close();
    return 0;
}