Codevita

import math
def fun():
    a=[]
    for i in range(0,10001):
        a.append(True)
    a[0]=a[1]=False
    x=math.ceil(math.sqrt(10001))
    for i in range(2,x):
        if(a[i]==True):
            for j in range(i*i,10001,i):
                a[j]=False
    return a
a=fun()
n1,n2=map(int,input().split())
l=[]
for i in range(n1,n2+1):
    if(a[i]==True):
        l.append(i)
n=len(l)
if(n!=0):
    m=[]
    for i in range(0,n):
        for j in range(0,n):
            if(i!=j):
                x=str(l[i])+str(l[j])
                if(a[int(x)]==True):
                    m.append(int(x))
    n=len(m)
    if(n!=0):
        m=list(set(m))
        n=len(m)
        m.sort()
        f1=m[0]
        f2=m[n-1]
        ans=0
        if(n==1):
            ans=f1
        elif(n==2):
            ans=f2
        else:
            for i in range(3,n+1):
                ans=f1+f2
                f1=f2
                f2=ans
            print(ans)