import sys
input = sys.stdin.readline

N, M = map(int, input().split())
ind = [[-1] * (N + 1) for i in range(M)]
for i in range(N * M):
    n, m = map(int, input().split())
    n, m = n - 1, m - 1
    ind[m][n] = i
    
for m in range(M):
    ind[m][-1] = ind[m][0]
   

def solve(A):
    now = 0
    card = 0
    cnt = 0
    while card != 5:
        nex = A[card]
        d = 5 - card
        n = (nex - now + d - 1)//d
        now += d * n
        cnt += n
        card = 0
        for i in range(5):
            if A[i] <= now:
                card += 1
    return cnt - 1
            
            

ans = 10 ** 18 
for m in range(M):
    for i in range(N - 3):
        L = []
        for j in range(5):
            L.append(ind[m][i + j])
        L.sort()
        ans = min(ans, solve(L))
        
print(ans)