n, m = map(int, input().split())

# Initialize a list to count the number of black cells in each column
black_counts = [0] * (n + 1)  # columns are 1-based

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

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

print(result)