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

int a[2000001];
int main() {
int b,c=0,i=2;
fin>>b;
if(b>=2 && b<=2000000){
while(i<=b)
{
    if(a[i]==0)
    {
        for(int j=i+i;j<=b;j+=i)

                {
                a[j]=1;
                }
            c++;
    }
            if(i==2)
            {
                i+=1;
            }else{i+=2;}
}
fout<<c;
}
return 0;
}