def pal(a, b):
    l = []
    max_score = 0
    max_pos = (0, 0)
    l.append([0]*(1+len(b)))
    for y, ca in enumerate(a):
        ll = [0]
        for x, cb in enumerate(b):
            if cb ==  ca:
                S = 1 + l[y][x]
                ll.append(S)
                if S > max_score:
                    max_pos = (y, x)
                    max_score = S
            else:
                ll.append(0)
        l.append(ll)

    for line in l:
        print(line)

    x, y = max_pos
    print(a[x-max_score+1:x+1])


s="bonjour_lol_gens"

pal(s, s[::-1])