#include <fstream>

using namespace std;

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

bool prim(int n)
{
    if(n == 2)
        return true;
    if(n % 2 == 0 || n == 1)
        return false;
    int d = 2;
    while(d * d <= n)
    {
        if(n % d == 0)
            return false;
        d += 2;
    }
    return true;
}

int main()
{
    int n;
    fin >> n;
    int cnt = -1;
    for(int i = 2; i <= n; i++)
        if(prim(i))
            cnt++;
    fout << cnt;
    return 0;
}