#include<iostream>
#include<fstream>
using namespace std;
int main()
{
    unsigned long n,i,j,c,a[2000000];
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for(i=1;i<=n;i++)
a[i]=0;

    c=0;
    for(i=3;i*i<=n;i+=2)
    if(a[i]==0)
    {for(j=i;j<=n;j+=i) a[j]=1;
    c++;}

    g<<c;
    f.close();
    g.close();
    return 0;
}