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)
