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

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

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

# Count 'c', 'o', 'n' in each group
g0_c = group0.count('c')
g0_o = group0.count('o')
g0_n = group0.count('n')

g1_c = group1.count('c')
g1_o = group1.count('o')
g1_n = group1.count('n')

g2_c = group2.count('c')
g2_o = group2.count('o')
g2_n = group2.count('n')

# Calculate each pattern's maximum possible
pattern0 = min(g0_c, g1_o, g2_n)
pattern1 = min(g1_c, g2_o, g0_n)
pattern2 = min(g2_c, g0_o, g1_n)

sum_patterns = pattern0 + pattern1 + pattern2

total_c = g0_c + g1_c + g2_c
total_o = g0_o + g1_o + g2_o
total_n = g0_n + g1_n + g2_n
total_min = min(total_c, total_o, total_n)

answer = min(sum_patterns, total_min)
print(answer)