Answer: Following code is in python
n=input()
num='1'
while int(num)<=int(n): //loop from 1 to n
flag=1 //if an unequal element will be found it will be 0
l=len(num)
if num[0]=='3':
j=0
k=l-1
while j<k: //loop till middle of number
if num[j]==num[k]:
j+=1 //from beginning
k-=1 //from end
else:
flag=0
break
if flag==1:
print(int(num))
num=str(int(num)+1) //number will be incremented as integer
INPUT :
1000
OUTPUT :
3
33
303
313
323
333
343
353
363
373
383
393
Step-by-step explanation:
In the above code, a loop is executed till num is equal to n which is entered by the user. num is treated as a string so that to ease the process of checking first character is 3 or not. If it is 3 then another loop executes which checks if an element from starting is equal to the corresponding element from the end. If an element is not equal then the flag is changed and then we break out of the loop and prints the number if the flag isn't changed.