/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
import java.util.Arrays;
import java.util.Scanner;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
  public static void main (String[] args) throws java.lang.Exception
  {
    //int n, m;  
    Scanner in = new Scanner(System.in);
 
     final int MAXN = 10000001;
     int simple[]=new int[MAXN+1];
     for(int i = 2; i <= MAXN; i++){
         simple[i] = 1;
     }
     for(int i = 2; i <= Math.sqrt(MAXN); i++){
         if(simple[i]==1){
             for(int j = i * i; j <= MAXN; j += i){
                 simple[j] = 0;
             }
         }
     }
 
     int count[]=new int[MAXN+1];
     int lastSum = 0;
     for(int i = 1; i < MAXN; i++){
         count[i] = lastSum + simple[i];
         lastSum = count[i];
     }
      while(in.hasNextInt()) {
        int m = in.nextInt();
    int n = in.nextInt();
        int answer = count[n] - count[m] + simple[m];
        System.out.println();
      System.out.println(answer);
      }
  }
}

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MiAyMAo3MCAxMTAKNSAxNTA=

2 20
70 110
5 150