#include<iostream>
using namespace std;
int main()
{
	int a,b,n,p,d,s=0;
	cout<<"a="; cin>>a;
	cout<<"b="; cin>>b;
	for(n=a;n<=b;n++)
	{
		p=1;
		for(d=2;d<=n/2;d++)
			if(n%d==0) p=0;
		if(p==1) s=s+n;
	}
	cout<<s;
	return 0;
}