#include<iostream>
#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,i,j,v[2000001],s;
int main (){
    cin>>n;
    i=2;
    s=n-1;
    for(i=2;i*i<=n;i++){
        if(v[i]==0)
            for(j=i*i;j<=n;j=j+i){
                v[j]=1;
                s--;
            }
    }
    cout<<s;
     
    return 0;
}