#############################################################

import sys
sys.setrecursionlimit(10**7)

from heapq import heappop,heappush
from collections import deque,defaultdict,Counter
from bisect import bisect_left, bisect_right
from itertools import product,combinations,permutations

ipt = sys.stdin.readline

def iin():
    return int(ipt())
def lmin():
    return list(map(int,ipt().split()))

MOD = 998244353
#############################################################

N,M = lmin()
L = [lmin() for _ in range(N*M)]
idx = [[0]*N for _ in range(M)]
for i,(n,m) in enumerate(L):
    idx[m-1][n-1] = i

ans = 1<<60
for i in range(M):
    for j in range(N-3):
        T = []
        cnt = 0
        tmp = 0
        for k in range(5):
            if idx[i][(j+k)%N] < 5:
                cnt += 1
            else:
                T.append(idx[i][(j+k)%N])
        T.sort(reverse=True)
        #print(T)
        cur = 4
        while T:
            #print(cur,cnt,tmp)
            if cnt == 4:
                d = T[-1]-cur
            else:
                d = (T[-1]-cur+5-cnt-1)//(5-cnt)
            nxt = cur+d*(5-cnt)
            tmp += d
            while T and T[-1] <= nxt:
                T.pop()
                cnt += 1
            cur = nxt
        #print(tmp)
        ans = min(ans,tmp)


#print(idx)
print(ans)