#include <fstream>
using namespace std;

int n;
int i = 0,j=0,p=0,v[2000000],nr = 1;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool prim(int n)
{
    int ok = 1;
    for(int d = 3; d*d <= n; d += 2) {
        if(n % d == 0) return false;
    }
    return true;
}

int main()
{
    int n, cont = 0;
    fin >> n;
    if(n >= 2) {
        ++cont;
        for(int i = 3; i <= n; i += 2)
            if(prim(i)) ++cont;
    }
    fout << cont;
}