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

from collections import defaultdict

groups = {
    0: {'c': 0, 'o': 0, 'n': 0},
    1: {'c': 0, 'o': 0, 'n': 0},
    2: {'c': 0, 'o': 0, 'n': 0}
}

for i in range(len(s)):
    mod = i % 3
    c = s[i]
    if c in ['c', 'o', 'n']:
        groups[mod][c] += 1

c0, o0, n0 = groups[0]['c'], groups[0]['o'], groups[0]['n']
c1, o1, n1 = groups[1]['c'], groups[1]['o'], groups[1]['n']
c2, o2, n2 = groups[2]['c'], groups[2]['o'], groups[2]['n']

t1 = min(c0, o1, n2)
t2 = min(c1, o2, n0)
t3 = min(c2, o0, n1)

total = t1 + t2 + t3

print(total)