#include <fstream>

using namespace std;

ifstream ci ("ciur.in");
ofstream co ("ciur.out");

int v[2000000];

int main()
{
    int n, r=0;
    ci >> n;
    if (n>=2)
    {
        r++;
    }
    for (int i=3; i<=n; i+=2)
    {
        if (v[i]==0)
        {
            r++;
            for (int j=i*i; j<=n; j+=i)
            {
                v[j]=1;
            }
        }
    }
    co << r;
    return 0;
}