#include <fstream>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool v[2000000];

int main ()
{
    unsigned long n,i,j,s=0;
    fin>>n;
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
            s++;
            for(j=i*i;j<=n;j+=i)
                v[j]=1;
        }
    }
    fout<<s;
}