#include<iostream>
#include<fstream>
#include<math.h>
using namespace std;
int n,nr_div,contor,k=2;
bool v[2000001];
int main(){
ifstream f("ciur.in");
ofstream g("ciur.out");
f>>n;
for(int i=2;i<=n;i++){
    if(v[i]==false)
    for(int j=i*2;j<=n;j=j+i)
        v[j]=true;

}
for(int i=2;i<=n;i++)
    if(v[i]==false)
        contor++;
g<<contor;
}