import sys
input = sys.stdin.readline

N,M=map(int,input().split())

dif = [0]*N
for _ in range(M):
    u,v=map(lambda x:int(x)-1,input().split())
    dif[u]+=1
    dif[v]-=1
print(max(sum([abs(d) for d in dif])//2-1,0))