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

dat = [[0] * 3 for _ in range(3)]
for i in range(NN):
    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])
"""
ans += min(dat[0][0],dat[1][1],dat[2][2])
t = min(dat[1][0],dat[2][1],dat[0][2])
if t == N:
    t -= 1
ans += t
t = min(dat[2][0],dat[0][1],dat[1][2])
if t == N:
    t -= 1
ans += t
print(ans)