l=["carbon","car","carrot"]
l.sort(key=lambda x:len(x))
result,m="",0
for index in range(len(l[0])):
    for item in range(1,len(l)):
        if l[0][index]!=l[item][index]:
            m=1
            break
    if m==1:
        break
    result+=l[0][index]
print(result)