#include <fstream>

using namespace std;

int n,d;
char ciur[2000005];

int main()
{
    int i, j;

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

    f>>n;
    for (i = 2; i<=n; ++i)
        ciur[i] = 1;
    for (i = 2; i<=n; ++i)
        if (ciur[i])
        {
            d++;
            for (j = i+i; j<=n; j += i)
                ciur[j] = 0;
        }

     g<<d;

    return 0;
}