'''
Problem Description
Given two numbers n1 and n2

1. Find prime numbers between n1 and n2, then

2. Make all possible unique combinations of numbers from the prime 
numbers list you found in step 1. 

3. From this new list, again find all prime numbers.

4. Find smallest (a) and largest (b) number from the 2nd generated 
list, also count of this list.

5. Consider smallest and largest number as the 1st and 2nd number 
to generate Fibonacci series respectively till the count 
(number of primes in the 2nd list).

6. Print the last number of a Fibonacci series as an output

Constraints
2 <= n1, n2 <= 100

n2 - n1 >= 35

Input Format
One line containing two space separated integers n1 and n2.

Output
Last number of a generated Fibonacci series.

Timeout
1


Test Case
Example 1
Input : 2 40
Output : 13158006689

Explanation :

1st prime list = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]

Combination of all the primes = [23, 25, 27, 211, 213, 217, 219, 
223, 229, 231, 32, 35, 37, 311, 313, 319, 323, 329, 331, 337, 52, 
53, 57, 511, 513, 517, 519, 523, 529, 531, 537, 72, 73, 75, 711, 
713, 717, 719, 723, 729, 731, 737, 112, 113, 115, 117, 1113, 1117, 
1119, 1123, 1129, 1131, 1137, 132, 133, 135, 137, 1311, 1317, 1319, 
1323, 1329, 1331, 1337, 172, 173, 175, 177, 1711, 1713, 1719, 1723, 
1729, 1731, 1737, 192, 193, 195, 197, 1911, 1913, 1917, 1923, 1929, 
1931, 1937, 232, 233, 235, 237, 2311, 2313, 2317, 2319, 2329, 2331, 
2337, 292, 293, 295, 297, 2911, 2913, 2917, 2919, 2923, 2931, 2937, 
312, 315, 317, 3111, 3113, 3117, 3119, 3123, 3129, 3137, 372, 373, 
375, 377, 3711, 3713, 3717, 3719, 3723, 3729, 3731]

2nd prime list=[193, 3137, 197, 2311, 3719, 73, 137, 331, 523, 
1931, 719, 337, 211, 23, 1117, 223, 1123, 229, 37, 293, 2917, 
1319, 1129, 233, 173, 3119, 113, 53, 373, 311, 313, 1913, 1723, 
317]

smallest (a) = 23

largest (b) = 3719

Therefore, the last number of a Fibonacci series i.e. 34th 
Fibonacci number in the series that has 23 and 3719 as the first 
2 numbers is 13158006689

Example 2
Input : 30 70
Output : 2027041 

Explanation

1st prime list=[31, 37, 41, 43, 47, 53, 59, 61, 67]

2nd prime list generated form combination of 1st prime list = [3137, 
5953, 5347, 6761, 3761, 4337, 6737, 6131, 3767, 4759, 4153, 3167, 
4159, 6143]

smallest prime in 2nd list=3137
largest prime in 2nd list=6761

Therefore, the last number of a Fibonacci series i.e. 14th 
Fibonacci number in the series that has 3137 and 6761 as the first 
2 numbers is 2027041
'''

import math
n1, n2 = map(int, input().split())
l = [i for i in range(n2+1)]
l[1] = 0

for i in range(2,n2+1):
  if(l[i]==i):
    for j in range(2*i, n2+1, i):
      l[j] = 0

k = []
for i in l:
  if (i!=0 i>=n1):
    k.append(i)
    
s = set()
for i in range(len(k)-1):
  for j in range(i+1, len(k)):
    s.add(int(str(k[i])+str(k[j])))
    s.add(int(str(k[j])+str(k[i])))
    
k = list(s)
k.sort()

minn = k[0]
maxx = k[-1]

m = [i for i in range(maxx+1)]
m[1] = 0
for i in range(2, maxx+1):
  if (m[i] == i):
    for j in range(2*i, maxx+1, i):
      m[j] = 0
      
prim2list = []
for i in m:
  if i>=minn and i in s:
    prim2list.append(i)
    
minn = prim2list[0]
maxx = prim2list[-1]
lenn = len(prim2list)

cnt = 2
while (cnt<lenn):
  tmp = minn
  minn = maxx
  maxx = tmp+maxx
  cnt+=1
print(maxx)