n=int(input())
s=list(input())
from _collections import defaultdict
cnt=defaultdict(int)
for i in range(3*n):
    cnt[i%3,s[i]]+=1
ans=0
for j in range(3):
    res=min(cnt[j,"c"],cnt[(j+1)%3,"o"],cnt[(j+2)%3,"n"])
    ans+=res
print(ans)