def mayorD(N, M=0):
if N == 0:
return M
if N % 10 > M:
M = N % 10
return mayorD(N // 10, M)
print(mayorD(91))
ZGVmIG1heW9yRChOLCBNPTApOgogICAgaWYgTiA9PSAwOgogICAgICAgIHJldHVybiBNCiAgICBpZiBOICUgMTAgPiBNOgogICAgICAgIE0gPSBOICUgMTAKICAgIHJldHVybiBtYXlvckQoTiAvLyAxMCwgTSkKCnByaW50KG1heW9yRCg5MSkp