n = int(input())
s = input()
con = [[0] * 3 for i in range(3)]
dat = ["c", "o", "n"]



for i in range(3*n):
	for j in range(3):
		if s[i] == dat[j]:
			con[i%3][j] += 1

#無駄なスペースを取らない
ans = 99999999
for i in range(3):
	ans = min(ans, con[i][i])

v = [n] * 3
for i in range(3):
	for j in range(3):
		v[i] -= con[(i+j)%3][i]

#無駄なスペースを1つ分とる
for i in range(64):
	mode = 1
	for j in range(3):
		typ = (i // (4 ** j)) % 4
		if typ == 3:
			if v[j] == 0:
				mode = 0
		else:
			con[j][typ] -= 1
			if con[j][typ] < 0:
				mode = 0
	
	tmp = 0
	for k in range(3):
		r = 999999
		for l in range(3):
			r = min(r, con[(l+k)%3][l])
		tmp += r
	
	if mode:
		ans = max(tmp, ans)
	
	for j in range(3):
		typ = (i // (4 ** j)) % 4
		if typ < 3:
			con[j][typ] += 1

print(ans)