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

from collections import defaultdict

groups = [defaultdict(int) for _ in range(3)]
for i in range(len(s)):
    g = i % 3
    c = s[i]
    groups[g][c] += 1

c0 = groups[0].get('c', 0)
o0 = groups[0].get('o', 0)
n0 = groups[0].get('n', 0)

o1 = groups[1].get('o', 0)
n2 = groups[2].get('n', 0)

c1 = groups[1].get('c', 0)
o2 = groups[2].get('o', 0)

c2 = groups[2].get('c', 0)
n1 = groups[1].get('n', 0)

term0 = min(c0, o1, n2, n)
term1 = min(c1, o2, n0, n - 1)
term2 = min(c2, o0, n1, n - 1)

print(term0 + term1 + term2)