


n=int(input())
st=[]
for i in range(n):
st.append(input())
for i in range(len(st[0])+1):
check=[]
for j in range(len(st)):
if st[j][-(i+1):] not in check:
check.append(st[j][-(i+1):])
else:
check=[]
break
if check!=[]:
print(i+1)
break