#include <iostream>
#include <fstream>

using namespace std;

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

int n, nr = 1;
int OK[2000010];

int main()
{
    in >> n;

    for (int i = 3; i <= n; i = i + 2)
    {
        if (OK[i] == 0)
        {
            for (unsigned long long j = i * i; j <= n; j = j + i)
                OK[j] = 1;
            OK[i] = 1;

            nr++;
        }
    }

    out << nr;

    return 0;
}