from itertools import permutations
n = int(input())
s = input()
ls = [[] for _ in range(3)]
for i in range(n*3):
  ls[i%3].append(s[i])
ans = 0
con = "con"
for i in range(3):
  res = 1 << 30
  for j in range(3):
    res = min(res, ls[(i+j)%3].count(con[j]))
  ans += res
print(ans)