l=["carbon","cart","carrot"]
l.sort(key=lambda x: len(x))
Common_Prefix,m="",1
for number in range(len(l[0])):
    scale=l[0][0:number+1]
    for word in l:
        if word.startswith(scale)==False:
            m=-1
            break
    if m==-1:
        break
    Common_Prefix=scale
print(word)