#include <iostream>
#include <fstream>

using namespace std;

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

int n, i, j, k, c;
short v[2000001];

int main()
{
    fin >> n;
    for (i = 2; i * i <= n; i++)
    {
        if(v[i] == 0)
        {
            c++;
            for (j = i * i; j <= n; j += i)
                v[j] = 1;
        }

    }
    fout << c;
    return 0;
}