import java.util.Scanner;
public class Main{
public int sc(int a){
int number=1;
for(int s=2;s<=Math.sqrt(a);s++) {
if(a%s==0){
number=0;
break;
}
}
return number;
}
public static void main(String[] args) {
int n,m,i=0;
int sum=0,j=0;;
Main scd=new Main();
Scanner sr1 = new Scanner(System.in);
Scanner sr2 = new Scanner(System.in);
n=sr1.nextInt();
m=sr2.nextInt();
for(i=2;;i++){
j+=scd.sc(i);
if(scd.sc(i)==1){
if(n<=j&&j<=m){
sum+=i;
if(j==m) {
break;
}
}
}
}
System.out.println(sum);
}
}
浮点数存在误差,不要 s<=Math.sqrt(a) 这么比较