n, m = map(int, input().split())
count_black = [0] * (n + 1)  # 1-based indexing for columns

for _ in range(m):
    r, c = map(int, input().split())
    count_black[c] += 1

result = 0
for c in range(1, n + 1):
    black = count_black[c]
    white = n - black
    result += min(black, white)

print(result)