1 #include <bits/stdc++.h>
2 using namespace std;
3 const int maxv = 110;
4 const int maxe = 110*110;
5 const int inf = 0x3f3f3f3f;
6 struct Edge{
7 int u, v, nex;
8 int cap, flow;
9 Edge(int u=0, int v=0, int nex=0, int cap=0, int flow=0):
10 u(u), v(v), nex(nex), cap(cap), flow(flow){}
11 }e[maxe<<1];
12 int head[maxv];
13 int cnt;
14 void init(){
15 memset(head, -1, sizeof(head));
16 cnt = 0;
17 }
18
19 void add(int u, int v, int cap){
20 e[cnt] = Edge(u, v, head[u], cap, 0);
21 head[u] = cnt++;
22 e[cnt] = Edge(v, u, head[v], 0, 0);
23 head[v] = cnt++;
24 }
25
26 int d[maxv], num[maxv], cur[maxv], p[maxv];
27 int vis[maxv];
28 int S, T;
29 int N;
30
31 void bfs(){
32 memset(d, -1, sizeof(d));
33 memset(vis, 0, sizeof(vis));
34 queue<int> q;
35 q.push(T);
36 vis[T] = 1;
37 d[T] = 0;
38 while(!q.empty()){
39 int u = q.front();
40 q.pop();
41 for(int i = head[u]; ~i; i = e[i].nex){
42 int id = i&(-2); //正边
43 int v = e[id].u;
44 if(!vis[v] && e[id].cap > e[id].flow){
45 vis[v] = 1;
46 d[v] = d[u] + 1;
47 q.push(v);
48 }
49 }
50 }
51 }
52
53 int augment(){
54 int u = T;
55 int a = inf;
56 while(u!=S){
57 int id = p[u];
58 a = min(a, e[id].cap - e[id].flow);
59 u = e[id].u;
60 }
61 u = T;
62 while(u!=S){
63 int id = p[u];
64 e[id].flow += a;
65 e[id^1].flow -= a;
66 u = e[id].u;
67 }
68 return a;
69 }
70
71 int ISAP(){
72 bfs();
73 int flow = 0;
74 memset(num, 0, sizeof(num));
75 for(int i = 0; i < N; i++){
76 cur [i] = head[i];
77 if(~d[i]) num[d[i]]++;
78 }
79 int u = S;
80 while(d[S] < N){
81 if(u == T){
82 flow += augment();
83 u = S;
84 }
85 int ok = 0;
86 for(int i = cur[u]; ~i; i = e[i].nex){
87 int v = e[i].v;
88 if(d[u] == d[v]+1 && e[i].cap > e[i].flow){
89 p[v] = i;
90 ok = 1;
91 cur[u] = i;
92 u = v;
93 break;
94 }
95 }
96 if(!ok){
97 int m = N-1;
98 for(int i = head[u]; ~i; i = e[i].nex){
99 if(e[i].cap > e[i].flow && ~d[e[i].v]) m = min(m, d[e[i].v]);
100 }
101 if(--num[d[u]] == 0) break;
102 num[d[u]=m+1]++;
103 cur[u] = head[u];
104 if(u != S) u = e[p[u]].u;
105 }
106 }
107 return flow;
108 }
109
110 int main(){
111 int n, m;
112 init();
113 scanf("%d %d", &m, &n);
114 int u, v;
115 while(scanf("%d %d", &u, &v)){
116 if(u==-1 && v==-1) break;
117 add(u,v,1);
118 }
119 S = 0; T = n+1;
120 N = T+1;
121 for(int i = 1; i <= m; i++){
122 add(S, i, 1);
123 }
124 for(int i = m+1; i <= n; i++){
125 add(i, T, 1);
126 }
127 int ans = ISAP();
128 printf("%d\n", ans);
129 }
