1 #include<bits/stdc++.h>
2 #define _for(i,a,b) for(register int i = (a);i < b;i ++)
3 #define _rep(i,a,b) for(register int i = (a);i > b;i --)
4 #define INF 0x3f3f3f3f
5 #define MOD 100000000
6 #define maxn 100003
7 #define pb push_back
8 #define debug() printf("Miku Check OK!\n")
9 typedef long long ll;
10
11 using namespace std;
12 typedef pair<int,int> P;
13 inline ll read()
14 {
15 ll ans = 0;
16 char ch = getchar(), last = ' ';
17 while(!isdigit(ch)) last = ch, ch = getchar();
18 while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar();
19 if(last == '-') ans = -ans;
20 return ans;
21 }
22 inline void write(ll x)
23 {
24 if(x < 0) x = -x, putchar('-');
25 if(x >= 10) write(x / 10);
26 putchar(x % 10 + '0');
27 }
28 int ver[maxn],Next[maxn],head[maxn],val[maxn];
29 int d[maxn];
30 int n,m,s,t,tot,maxflow;
31 void add(int x,int y,int w)
32 {
33 ver[++tot] = y,Next[tot] = head[x],head[x] = tot,val[tot] = w;
34 }
35 bool bfs()
36 {
37 memset(d,0,sizeof(d));
38 queue<int> q;
39 q.push(s);d[s] = 1;
40 while(!q.empty())
41 {
42 int x = q.front();q.pop();
43 for(int i = head[x]; i; i = Next[i])
44 if(val[i] && !d[ver[i]])
45 {
46 q.push(ver[i]);
47 d[ver[i]] = d[x]+1;
48 if(ver[i]==t)
49 return true;
50 }
51 }
52 return false;
53 }
54 int dinic(int x,int flow)
55 {
56 if(x==t) return flow;
57 // k为子节点增量
58 int rest = flow, k;
59 for(int i = head[x]; i && rest; i = Next[i])
60 {
61 if(val[i] && d[ver[i]] == d[x]+1)
62 {
63 k = dinic(ver[i],min(rest,val[i]));
64 if(!k) d[ver[i]] = 0;
65 val[i] -= k;
66 val[i^1] += k;
67 rest -= k;
68 }
69 }
70 return flow - rest;
71 }
72 vector<int> st;
73 int vvis[maxn];
74 void go(int i,vector<int>& rnt)
75 {
76 rnt.pb(i);
77 for(int j = head[i]; j ; j = Next[j])
78 {
79 int y = ver[j];
80 if(y>n && !vvis[y-n] && !val[j])
81 {
82 vvis[y-n] = 1;
83 go(y-n,rnt);
84 }
85 }
86 }
87 int main()
88 {
89 n = read();m = read();
90 tot = 1;maxflow = 0;s = 0;t = 2*n+1;
91 _for(i,1,m+1)
92 {
93 int x = read();int y = read();
94 add(x,y+n,1);add(y+n,x,0);
95 }
96 _for(i,1,n+1)
97 {
98 add(0,i,1);add(i,0,0);
99 add(i+n,2*n+1,1);add(2*n+1,i+n,0);
100 }
101 int flow = 0;
102 while(bfs())
103 while(flow = dinic(s,INF))
104 maxflow += flow;
105 vvis[0] = 1;
106 _for(i,1,n+1)
107 {
108 for(int j = head[i+n]; j ; j = Next[j])
109 if(ver[j]==2*n+1 && val[j]==1)
110 st.pb(i),vvis[i] = 1;
111 }
112
113 vector<int> tmp;
114 _for(i,0,st.size())
115 {
116 vvis[st[i]] = 1,go(st[i],tmp);
117 _for(j,0,tmp.size()-1)
118 printf("%d ",tmp[j]);
119 printf("%d\n",tmp[tmp.size()-1]);
120 tmp.clear();
121 }
122
123 write(n-maxflow);
124 return 0;
125 }
