My code in python 3.6:

def is_palindrom(x):
    if x==x[::-1]:
        return True
    return False

s=input()
s=s[::-1]
n=len(s)
a=[]
for x in range(2,n+1):
    for i in range(0,n-x+1):
        if is_palindrom(s[i:i+x]):
            a.append(s[i:i+x])
if len(a)==0:
    b=s[-1]
else:
    b=a[-1]
print(b)

Memory is 70160 Kb, where so much it?
Please, help, I would be grateful!