n=int(eval(input()))

a= list(eval(input()))

b= list(eval(input()))

c= list(eval(input()))



alphabet = [chr(i) for i in range(97, 97+26)]



ans = 0

for i in range(n):

    cnt = 200

    for j in range(26):

        cnt_tmp = 0

        if (a[i] != alphabet[j]):

            cnt_tmp += 1

        if (b[i] != alphabet[j]):

            cnt_tmp += 1

        if (c[i] != alphabet[j]):

            cnt_tmp += 1

        cnt = min(cnt, cnt_tmp)

    ans += cnt



print(ans)

    

        

        



'''

west

east

wait

'''







n=int(eval(input()))

a= list(eval(input()))

b= list(eval(input()))

c= list(eval(input()))



ans = 0

for i in range(n):

    ans += len({a[i], b[i], c[i]}) - 1



print(ans)

    

        

        



'''

west

east

wait



{'w', 'e', 'w'}

{'w', 'e'}

len → 2 

1文字は使って良い -1





'''
n = int(eval(input()))
a = list(eval(input()))
b = list(eval(input()))
c = list(eval(input()))
alphabet = [chr(i) for i in range(97, 97 + 26)]
ans = 0
for i in range(n):
    cnt = 200
    for j in range(26):
        cnt_tmp = 0
        if a[i] != alphabet[j]:
            cnt_tmp += 1
        if b[i] != alphabet[j]:
            cnt_tmp += 1
        if c[i] != alphabet[j]:
            cnt_tmp += 1
        cnt = min(cnt, cnt_tmp)
    ans += cnt
print(ans)
"""
west
east
wait
"""

n = int(eval(input()))
a = list(eval(input()))
b = list(eval(input()))
c = list(eval(input()))
ans = 0
for i in range(n):
    ans += len({a[i], b[i], c[i]}) - 1
print(ans)
"""
west
east
wait
{'w', 'e', 'w'}
{'w', 'e'}
len → 2 
1文字は使って良い -1
"""

-alphabet = [chr(i) for i in range(97, 97 + 26)] -    cnt = 200 -    for j in range(26): -        cnt_tmp = 0 -        if a[i] != alphabet[j]: -            cnt_tmp += 1 -        if b[i] != alphabet[j]: -            cnt_tmp += 1 -        if c[i] != alphabet[j]: -            cnt_tmp += 1 -        cnt = min(cnt, cnt_tmp) -    ans += cnt +    ans += len({a[i], b[i], c[i]}) - 1 +{'w', 'e', 'w'} +{'w', 'e'} +len → 2 +1文字は使って良い -1