from functools import reduce

f = lambda _i, _s: reduce(lambda i, s: i+2 if s=='1' else i*3, [_i, *_s])

print(f(0, '12'))         # 6
print(f(1,  '21211'))     # 19
print(f(1,  '22222'))     # 243
print(f(-5, '12121212'))  # -165