m = int(input())
s = input()
c = [s[i::3].count("c") for i in range(3)]
o = [s[i::3].count("o") for i in range(3)]
n = [s[i::3].count("n") for i in range(3)]
ans = 0
for i in range(3): ans += min(c[i], o[(i+1)%3], n[(i+2)%3])
print(ans)