import collections
N,M=map(int,input().split())
b=[ list(map(int,input().split())) for i in range(N) ]
c=[]
count=0
for i in b:
    c.append(i[1])

w=collections.Counter(c)

for i in w.values():
    if i >= 2:
        count += i//2 + i % 2

print(count)