# your code goes here
def isprime(n) :
if (n <= 1) :
return False
if (n <= 3) :
return True
if (n % 2 == 0 or n % 3 == 0) :
return False
i = 5
while(i * i <= n) :
if (n % i == 0 or n % (i + 2) == 0) :
return False
i = i + 6
return True
n1, n2 = map(int, input().split())
a = []
e = 0
g = 0
j = 0
k = []
#if(n1 == 2):
#a.append(n1)
for i in range(n1, n2+1):
if(isprime(i) == True):
a.append(i)
#print(a)
#print(len(a))
b = []
s = ''
for i in range(len(a)):
for j in range(len(a)):
if(a[i] != a[j]):
s = str(a[i])+str(a[j])
b.append(int(s))
s = ''
b = set(b)
b = list(b)
c = []
#print(b)
#print(len(b))
for i in range(len(b)):
if(isprime(b[i]) == True):
c.append(b[i])
#print(c)
#print(len(c))
c.sort()
e = c[0]
g = c[-1]
h = len(c)
#print(e,g)
for i in range(2,h):
j = e+g
e = g
g = j
#k.append(j)
#if(j > 10**15):
# j = j%mod
print(j)
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