#include <bits/stdc++.h>
using namespace std;
int par[200010]; 
int depth[200010]; 
int siz[200010];  
void init(){
	for(int i = 0; i < 200005; i++){
		par[i] = i; depth[i] = 0; siz[i] = 1; 
	}
}
int find(int x){
	if(par[x] == x) return x;
	else return par[x] = find(par[x]); 
}
void unite(int x, int y){
	x = find(x); 
	y = find(y); 
	if(x == y) return;
	else if(depth[x] < depth[y]){
		par[x] = y; 
		siz[y] += siz[x]; 
	}else{
		par[y] = x; 
		siz[x] += siz[y];  
		if(depth[x] == depth[y]) depth[x] ++; 
	}
}
bool same(int x, int y){
	return find(x) == find(y); 
}
int sz(int x){
	return siz[find(x)]; 
}
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);
	init();
	int N, M; cin >> N >> M;
	int deg[200010] = {}; 
	int A[200010], B[200010];
	for(int i = 0; i < M; i++){
		cin >> A[i] >> B[i]; unite(A[i], B[i]);
		deg[A[i]] ++; deg[B[i]] --;
	}
	int cmp = 0;
	int sum[200010] = {};
	bool seen[200010] = {};
	bool exist[200010] = {};
	for(int i = 0; i < M; i++){
		exist[find(A[i])] = true;
	}
	int ans = 0;
	for(int i = 1; i <= N; i++){
		if(deg[i] > 0) sum[find(i)] += deg[i];
	}
	for(int i = 1; i <= N; i++){
		if(seen[find(i)] || !exist[find(i)]) continue;
		ans += max(sum[find(i)] - 1, 0);
		cmp ++;
		seen[find(i)] = true;
	}
	cout << ans + cmp - 1 << "\n";
}