#include<cstdio>

 #include<algorithm>

 using namespace std;

 bool vis[];

 int a,b; long long ans;

 void Shai()

 {

     vis[]=true;

     for(long long i=;i<=;i++)

       for(long long j=i*i;j<=;j+=i)

         vis[j]=true;

 }

 int main()

 {

     scanf("%d%d",&a,&b); Shai(); if(a>b) swap(a,b);

     for(int i=a+;i<b;i++) if(!vis[i]) ans+=(long long)i;

     printf("%lld\n",ans);

     return ;

 }