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#include <cstdio>
#include <cmath>
#include <algorithm>
#include <cstring>
using namespace std;
#define ll long long
#define R register
#define I inline
template<class >void read( &x) {
register ll c = getchar(), f = 1; x = 0;
while(!isdigit(c)) {if (c == '-') f = -1; c = getchar();}
while(isdigit(c)) x = x * 10 + c - '0', c = getchar();
x *= f;
}
const int maxn=100100,maxm=200200;
int dp[maxn],ind[maxn],outd[maxn];
struct edge {
int v,c;
edge *next;
}*h[maxn],pool[maxm];
int tot;
void addEdge(int u,int v)
{
edge *p=&pool[++tot];
p->v=v;p->next=h[u];h[u]=p;
ind[v]++;outd[u]++;
}
void dfs(int u)
{
if(dp[u]) return ;
if(outd[u]==0) {
dp[u]=1;
return ;
}
for(edge *p=h[u];p;p=p->next)
{
int v=p->v;
dfs(v);
dp[u]+=dp[v];
}
}
int n,m,ans;
int main()
{
read(n);read(m);
while(m--)
{
int u,v;
read(u);read(v);
addEdge(u,v);
}
for(int i=1;i<=n;i++)
if(!ind[i] && outd[i]) dfs(i),ans+=dp[i];
printf("%dn",ans);
return 0;
}
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