#include<iostream>
#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
const int NMAX=2000001;
int a[NMAX],N;
int main(){
fin>>N;
a[0]=a[1]=1;
for(int i=2;i*i<=N;i++)
    if(a[i]==0)
    for(int j=2;j<=N/i;j++)
    a[i*j]=1;
int total=0;
    for(int i=1;i<=N;i++)
if(a[i]==0)
    total++;
fout<<total;
fin.close();
fout.close();
return 0;}