import java.util.*;
import java.util.Collections;
public class Main {
public static void main
(String[] args
) { Scanner sc
=new Scanner
(System.
in); int n=sc.nextInt();
boolean [] primes=new boolean [n+1];
int count=0;
for(int i=2;i<n;i++){
if(primes[i]){
count++;
for(int j=2*i;j<n;j+=i){
if(j%i==0) primes[j]=false;
}
}
}
}
}
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