https://www.luogu.com.cn/record/164563240

#include<iostream>
#include<queue>
#include<vector>
#include<algorithm>
#include<cstdio>
#include<cstring>
#define int long long

struct edge{
	int v,w;
};
const int MD=80'112'002;
const int N=1510;
using namespace std;
queue<int>q;
vector<edge>e[N];
int f[N],p[N],t[N],s[N],vis[N];
int n,m;
void top(){
	q.push(1);
	f[1]=0;
	while(!q.empty()){
		int u=q.front();q.pop();
		for(int i=0;i<e[u].size();i++){
			int v=e[u][i].v,w=e[u][i].w;
			p[v]--;
			f[v]=max(f[u]+w,f[v]);
			if(p[v]==0)q.push(v);
		}
	}
}
signed main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++)f[i]=-1e18;
	for(int i=1;i<=m;i++){
		int u,v,w;
		cin>>u>>v>>w;
		e[u].push_back((edge){v,w});
		p[v]++;
	}
	top();
//	for(int i=1;i<=n;i++)cout<<f[i]<<endl;
	if(f[n]==-1e18)cout<<-1<<endl;
	else cout<<f[n]<<endl;
}