iterative tribonacci python
def trib_iter(m):
lista=[m]
c=0
d=True
while d==True:
novalista=[]
for n in lista:
if n in [0,1,2]:
c+=1
else:
for i in range(1,4):
if n-i in [0,1,2]:
c+=1
else:
if n-i<0:
pass
else:
novalista.append(n-i)
if novalista==[]:
d=False
else:
lista=novalista
return c