paste bin

def mirrorNum(x):
    return int(str(x)[::-1])

UPBD=10003
isPrime = [True for _ in range(UPBD)]

isPrime[0]=False
isPrime[1]=False

for i in range(UPBD):
    if isPrime[i]==False:
        continue
    k=i*i
    while k<UPBD:
        isPrime[k]=False
        k+=i

a,b = map(int,input().split())
count=0
for i in range(a,b+1):
    if isPrime[i] and isPrime[mirrorNum(i)]:
        count+=1;

print(count)