AC样例，评测......

#include<bits/stdc++.h>
using namespace std;

int a[5010][10010],cnt[5010];
long long dp[5010];

int main()
{
    int n,m;
    cin >> n >> m;
    for(int i = 1;i <= m;i++)
    {
        int x,y;
        cin >> x >> y;
        a[y][++cnt[y]] = x;
    }
    for(int i = 1;i <= n;i++)
    {
        for(int j = 1;j <= cnt[i];j++) dp[i] += dp[a[i][j]];
        dp[i] = max(dp[i],1ll) % 80112002;
    }
    for(int i = n;i;i--)
    {
        long long x = 0;
        for(int j = 1;j <= cnt[i];j++) x += dp[a[i][j]];
        dp[i] = max(dp[i],x) % 80112002;
    }
    for(int k = 1;k <= 10;k++)
    {
        for(int i = 1;i <= n;i++)
        {
            long long x = 0;
            for(int j = 1;j <= cnt[i];j++) x += dp[a[i][j]];
            dp[i] = max(dp[i],x) % 80112002;
        }
        for(int i = n;i;i--)
        {
            long long x = 0;
            for(int j = 1;j <= cnt[i];j++) x += dp[a[i][j]];
            dp[i] = max(dp[i],x) % 80112002;
        }
    }
    cout << dp[n] % 80112002;
    return 0;
}