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

group0 = []
group1 = []
group2 = []

for i in range(len(s)):
    c = s[i]
    if i % 3 == 0:
        group0.append(c)
    elif i % 3 == 1:
        group1.append(c)
    else:
        group2.append(c)

def count_chars(g):
    c = o = n = 0
    for char in g:
        if char == 'c':
            c +=1
        elif char == 'o':
            o +=1
        elif char == 'n':
            n +=1
    return c, o, n

C0, O0, N0 = count_chars(group0)
C1, O1, N1 = count_chars(group1)
C2, O2, N2 = count_chars(group2)

a = min(C0, O1, N2)
b = min(C2, O0, N1)
c = min(C1, O2, N0)

total = a + b + c

C_total = C0 + C1 + C2
O_total = O0 + O1 + O2
N_total = N0 + N1 + N2

min_total = min(C_total, O_total, N_total)

print(min(total, min_total))