#include <iostream>
#include <fstream>
using namespace std;
int i,j,a[100],n,k=0;
int main (void)
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for (i=2;i<=n;i++) a[i]=1;
    for (i=2;i<=n;i++)
        if (a[i]==1)
        {
            k++;
            for (j=i+i;j<=n;j++)
                a[j]=0;
        }
    g<<k;
    return 0;
}