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 = [min(c[i], o[(i+1)%3], n[(i+2)%3]) for i in range(3)]
print(min(sum(ans), m-1) if ans[1] or ans[2] else sum(ans))