#include <fstream>
#include <cmath>

using namespace std;

int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    bool a[2000001];
    int nr=0, n, i, j;
    in>>n;
    for (i=2; i<=n; i++)
        a[i]=1;
    for (i=2; i<=sqrt(n); i++)
        if (a[i])
            for (j=i; j<=n/i; j++)
                a[i*j]=0;
    for (i=2; i<=n; i++)
        if (a[i]) nr++;
    out<<nr;
    return 0;
}