2AC，其他WA了TAT

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int MOD=81002002;
int n,m,ans=0;
vector<int>p[5005];
int ind[5005],otd[5005],f[5005];
queue<int>q;
signed main()
{
    cin>>n>>m;
    for(int i=0;i<m;i++)
    {
        int x,y;
        cin>>x>>y;
        p[x].push_back(y);
        otd[x]++;
        ind[y]++;
    }
    for(int i=1;i<=n;i++)
    {
        if(ind[i]==0)
        { q.push(i);
          f[i]=1;}
    }
    while(!q.empty())
    {
        int x=q.front();
        q.pop();
        for(int i=0;i<p[x].size();i++)
        {
            int y=p[x][i];
            f[y]=(f[y]+f[x])%MOD;
            ind[y]--;
            if(ind[y]==0)q.push(y);
        }
    }
    for(int i=1;i<=n;i++)
    {
        if(otd[i]==0)ans=(ans+f[i])%MOD;
    }
    cout<<ans;
    return 0;
}