from collections import defaultdict


n=int(input())
s=input()

ans=0
for x in range(3):
  y=(x+1)%3
  z=(x+2)%3
  cnt=[0]*3
  for i in range(3*n):
    if s[i]=='c' and i%3==x:
      cnt[0]+=1
    if s[i]=='o' and i%3==y:
      cnt[1]+=1
    if s[i]=='n' and i%3==z:
      cnt[2]+=1
  
  ans+=min(cnt)

print(ans)