n,m=map(int,input().split())
c=[[] for i in range(m)]
for i in range(n*m):
	s,t=map(int,input().split())
	s-=1
	t-=1
	c[t].append((i,s))
for i in range(m):
	c[i].sort()
a=n*m
for _ in range(2):
	for i in range(m):
		q=[-1]*(n+1)
		for p,x in c[i]:
			q[x]=p
			for j in range(x-4,x+1):
				if 0<=j<j+4<=n:
					g=[-1]+q[j:j+5]
					g.sort()
					if all([gg>=0 for gg in g[1:]]):
						b=0
						for k in range(5):
							b+=(g[k+1]-g[k]-1+5-k-1)//(5-k)
						a=min(a,b)
	for i in range(m):
		for j in range(len(c[i])):
			if c[i][j][1]==0:
				c[i][j]=(c[i][j][0],n)
print(a)