#include <iostream>
#include <fstream>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

int a[2000002];
int main() {
int b,c=0,aux;
fin>>b;
if(b>=2 && b<=2000000){
for(int i=2;i<=b;i++)
{
    if(a[i]==0)
    {
        c++;
        for(int j=i;j<=b;j+=i)
        {
            a[j]=1;
        }

    }
}
fout<<c;
}
return 0;
}