while True:
a,b,c,d = map(int,input().split())
if a == b == c == d == 0:
break
else:
cnt = 0
while True:
if a == b == c == d:
break
a,b,c,d = abs(a-b),abs(b-c),abs(c-d),abs(d-a)
cnt+=1
print(cnt)