import sys
input=lambda:sys.stdin.readline().rstrip()
N=int(input())
S=input()
targ='con'
mem=[[0 for i in range(3)] for j in range(3)]
for i in range(3*N):
	if S[i] in targ:
		mem[i%3][targ.find(S[i])]+=1
if mem[0][0]==mem[1][1]==mem[2][2]==N:
	print(N)
else:
	ans=0
	for i in range(3):
		temp=3*N
		for j in range(3):
			temp=min(mem[j][(i+j)%3],temp)
		ans+=temp
	print(ans)