#include <fstream>
#include <math.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
bool v[2000005];
int i,j,n,m,k,cont=0;;
int main()
{
    f>>n;
    v[1]=1;
    for (i=4; i<=n; i+=2)
        v[i]=1;

    for (i=3; i<=sqrt(n); i+=2)
    {
        if (v[i]==0)
            for (j=i+i; j<=n; j+=i)
            v[j]=1;
    }
    for (i=2; i<=n; i++)
        if(v[i]==0) cont++;
    g<<cont;


    return 0;
}