#include <fstream>
#include <bitset>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int x, n, i, j, out;
bitset <2000001> b;
int main()
{
    fin >> n;
    b.flip();
    b[0] = 0; b[1] = 0;
    for (i = 2; i <= n; i++)
    {
        if (b[i] == 1)
        {
            for (j = i*i; j <= n; j+=i)
                b[j] = 0;
            out++;
        }
    }
    fout << out;
    return 0;
}