#include <iostream>
#include <fstream>

#define nmax 2000001

using namespace std;

int n, rez;
bool A[nmax];

int main()
{
    ifstream fi("ciur.in");
    ofstream fo("ciur.out");

    fi >> n;

    for (int i = 2; i <= nmax; i++)
        if (A[i] == 0)
        {
            if (i <= n)
                rez++;
            else
                break;

            for (int j = 2 * i; j <= nmax; j += i)
                A[j] = 1;

        }

    fo << rez << "\n";

    fi.close();
    fo.close();

    return 0;
}