n = int(input())
S = input()
cnt = [[0] * 3 for _ in range(3)]
for i, s in enumerate(S):
    if s == "c":
        cnt[i % 3][0] += 1
    elif s == "o":
        cnt[i % 3][1] += 1
    elif s == "n":
        cnt[i % 3][2] += 1


ans = 0
for i in range(3):
    mi = 1 << 30
    for j in range(3):
        mi = min(mi, cnt[(i + j) % 3][j])
    ans += mi
print(ans)