n = int(input())
s = input().strip()

groups = [[0, 0, 0] for _ in range(3)]  # groups[mod][0] = 'c', groups[mod][1] = 'o', groups[mod][2] = 'n'

for i in range(len(s)):
    c = s[i]
    mod = i % 3
    if c == 'c':
        groups[mod][0] += 1
    elif c == 'o':
        groups[mod][1] += 1
    elif c == 'n':
        groups[mod][2] += 1

max_con = 0
for start_mod in range(3):
    c_mod = start_mod
    o_mod = (start_mod + 1) % 3
    n_mod = (start_mod + 2) % 3
    c = groups[c_mod][0]
    o = groups[o_mod][1]
    n = groups[n_mod][2]
    max_con += min(c, o, n)

print(max_con)