N = int(input())
N *= 3
S = input()

dat = [[0] * 3 for _ in range(3)]
for i in range(N):
    j = i % 3
    if S[i] == "c":
        dat[j][0] += 1
    elif S[i] == "o":
        dat[j][1] += 1
    elif S[i] == "n":
        dat[j][2] += 1
ans = 0
for i in range(3):
    ans += min(dat[i][0],dat[(i+1)%3][1],dat[(i+2)%3][2])
print(ans)