#include <bits/stdc++.h>
using namespace std;

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

int n, nr;
bitset<2000005> a;
void ciur()
{
    int i;
    nr = 1;
    a[1] = 1;
    a[0] = 1;
    for (i = 3; i <= n; i += 2)
        if (a[i] == 0)
        {
            nr++;
            for (int j = i; j <= n; j += 2 * i)
                a[j] = 1;
        }
}

int32_t main()
{
    fin >> n;
    ciur();
    fout << nr << '\n';
    return 0;
}