import sys
sys.setrecursionlimit(2*10**5)
N,M=map(int,input().split())
edge=[[] for _ in range(2*N)]
for i in range(M):
    a,b=map(int,input().split())
    edge[a-1].append(b-1)
    edge[b-1].append(a-1)

use=[False for _ in range(2*N)]
ans=0
def dfs(i):
    global use,ans
    use[i]=True
    con=False
    for e in edge[i]:
        if not use[e]:
            r=dfs(e)
            if r==True:
                con=True
    if con:
        ans+=1
        return False
    else:
        return True

for i in range(2*N):
    if not use[i]:
        dfs(i)
print(N-ans)