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

group0 = s[0::3]
group1 = s[1::3]
group2 = s[2::3]

c0 = group0.count('c')
o0 = group0.count('o')
n0 = group0.count('n')

c1 = group1.count('c')
o1 = group1.count('o')
n1 = group1.count('n')

c2 = group2.count('c')
o2 = group2.count('o')
n2 = group2.count('n')

type1 = min(c0, o1, n2)
type2 = min(c1, o2, n0)
type3 = min(c2, o0, n1)

print(type1 + type2 + type3)