#include<fstream.h>
int n,nr;
char prim[2000005];
int main()
{
    int i,j;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for (i=2;i<=n;i++)
        prim[i]=1;
    for (i=2;i<=n;i++)
        if(prim[i])
        {
            ++nr;
            for (j=2*i;j<=n;j+=i)
                prim[j]=0;
        }
     g<<nr;
    return 0;
}