1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstdlib>
 4 #include <cmath>
 5 #include <cstring>
 6 #include <algorithm>
 7 #include <queue>
 8 #include <stack>
 9 #include <vector>
10 #define MP(a, b) make_pair(a, b)
11 #define PB(a) push_back(a)
12 
13 using namespace std;
14 
15 typedef long long ll;
16 typedef pair<int ,int> pii;
17 typedef pair<unsigned int, unsigned int> puu;
18 typedef pair<int ,double> pid;
19 typedef pair<ll, int> pli;
20 
21 const int INF = 0x3f3f3f3f;
22 const double eps = 1e-6;
23 const int LEN = 10000+10;
24 int vis[LEN], n, m, cmp[LEN];
25 vector<int> Map[LEN], rMap[LEN], vs;
26 
27 void dfs(int v)
28 {
29     vis[v] = 1;
30     for(int i=0; i<Map[v].size(); i++){
31         if(!vis[Map[v][i]])dfs(Map[v][i]);
32     }
33     vs.PB(v);
34 }
35 
36 void rdfs(int v, int k)
37 {
38     vis[v] = 1;
39     cmp[v] = k;
40     for(int i=0; i<rMap[v].size(); i++){
41         if(!vis[rMap[v][i]])rdfs(rMap[v][i], k);
42     }
43 }
44 
45 int scc()
46 {
47     memset(vis, 0, sizeof vis);
48     vs.clear();
49     for(int i=1; i<=n; i++){
50         if(!vis[i])dfs(i);
51     }
52     memset(vis, 0, sizeof vis);
53     int k = 0;
54     for(int i=vs.size()-1; i>=0; i--){
55         if(!vis[vs[i]])rdfs(vs[i], k++);
56     }
57     return k;
58 }
59 
60 int main()
61 {
62 //    freopen("in.txt", "r", stdin);
63 
64     int a, b;
65     while(scanf("%d%d", &n, &m)!=EOF){
66         for(int i=0; i<LEN; i++)Map[i].clear();
67         for(int i=0; i<LEN; i++)rMap[i].clear();
68         for(int i=0; i<m; i++){
69             scanf("%d%d", &a, &b);
70             Map[a].PB(b);
71             rMap[b].PB(a);
72         }
73         int num = scc(), ans = 0, u = 0;
74         for(int i=1; i<=n; i++)if(cmp[i] == num-1){u = i;ans++;}
75         memset(vis, 0, sizeof vis);
76         rdfs(u, 0);
77         for(int i=1; i<=n; i++)if(!vis[i])ans = 0;
78         printf("%d\n", ans);
79     }
80     return 0;
81 }