#include <fstream>
using namespace std;

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

bool b[2000002];

void ciur (int n)
{
    b[0] = b[1] = 1;
    int i, j;
    for (i=2; i*i<=n; i++)
        if (!b[i])
            for (j=i*i; j<=n; j+=i)
                b[j] = 1;
}

int main ()
{
    int n;
    f>>n;
    ciur(n);
    int cnt = 0;
    for (int i = 2; i<=n; i++)
        if (b[i]==0) cnt++;
    g<<cnt;
    return 0;
}