#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n;
    f>>n;
    char a[n+2];
    int c=0,i,k;
    for (i=2;i<=n;i++)
        a[i]=1;
    for (i=2;i<=n;i++)
    {
        if (a[i])
        {
            c++;
            for (k=i+i;k<=n;k=k+i)
            {
               a[k]=0;
            }
        }
    }
    g<<c;
    f.close();
    g.close();
    return 0;
}