I,R=input,range
N=int(I())*3
S=I()
a=0
s="con"
for d in R(3):
	c=[0]*3
	for i in R(N):
		if S[i]==s[(i+d)%3]:c[i%3]+=1
	a+=min(min(c),N-a*3-d)
print(a)