#include <fstream>

using namespace std;

int a[2000000], n,h=1;

int main()
{
    int i, j;

    ifstream fin("ciur.in");
    fin>>n;
    fin.close();
    for(i = 3; i* i <= n; i++)
        if (a[i] == 0) // i este prim
            for (j = i * i; j <= n; j = j + 2*i)
                a[j] = 1;
    for (i = 3; i <= n; i += 2)
        if (a[i] == 0) h++;

    ofstream fout("ciur.out");
    fout<<h<<"\n";
    fout.close();

    return 0;
}