#include <fstream>
#include <cmath>

using namespace std;

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

const int NMAX = 2000005;

bool prime[NMAX];

int main()
{
    int n,i,j;

    f>>n;

    int k=n-1;
    for(i=2;i<=n;++i)
        prime[i]=true;

    for(i=2;i<=sqrt(n);++i)
        if(prime[i]==true)
        for(j=i+i;j<=n;j+=i)
            if(prime[j]==true)
            {
                prime[j]=false;
                k--;
            }

    g<<k<<'\n';

return 0;
}