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

groupA = []
groupB = []
groupC = []

for i in range(len(s)):
    if i % 3 == 0:
        groupA.append(s[i])
    elif i % 3 == 1:
        groupB.append(s[i])
    else:
        groupC.append(s[i])

count_A_c = groupA.count('c')
count_A_o = groupA.count('o')
count_A_n = groupA.count('n')

count_B_c = groupB.count('c')
count_B_o = groupB.count('o')
count_B_n = groupB.count('n')

count_C_c = groupC.count('c')
count_C_o = groupC.count('o')
count_C_n = groupC.count('n')

max0 = min(count_A_c, count_B_o, count_C_n)
max1 = min(count_B_c, count_C_o, count_A_n)
max2 = min(count_C_c, count_A_o, count_B_n)

total = max0 + max1 + max2
print(total)