1 #include<iostream>
2 #include<cstdio>
3 #include<cstring>
4 #include<queue>
5 using namespace std;
6 struct edge{
7 int to;
8 int next;
9 int len;
10 }qwq[100005];
11 queue<int>pq;
12 int edge_cnt=0,n,m,head[100005],in[100005],stk[100005],dist[100005];
13 bool spfa()
14 {
15 memset(in,0,sizeof(in));
16 memset(stk,0,sizeof(stk));
17 memset(dist,-1,sizeof(dist));
18 dist[0]=0;
19 while(!pq.empty())
20 {
21 pq.pop();
22 }
23 pq.push(0);
24 in[0]++;
25 stk[0]=1;
26 while(!pq.empty())
27 {
28 int qaq=pq.front();pq.pop();
29 stk[qaq]=0;
30 for(int i = head[qaq];i!=-1;i=qwq[i].next)
31 {
32 int v=qwq[i].to;
33 if(dist[v]<dist[qaq]+qwq[i].len)
34 {
35 dist[v]=dist[qaq]+qwq[i].len;
36 if(!stk[v])
37 {
38 pq.push(v);
39 in[v]++;
40 stk[v]=1;
41 if(in[v]>n+1){
42 return false;
43 }
44 }
45 }
46 }
47 }
48 return true;
49 }
50 void add(int x,int y,int z)
51 {
52 qwq[edge_cnt].to=y;
53 qwq[edge_cnt].next=head[x];
54 qwq[edge_cnt].len=z;
55 head[x]=edge_cnt++;
56 }
57 int main()
58 {
59 scanf("%d%d",&n,&m);
60 memset(head,-1,sizeof(head));
61 edge_cnt=0;
62 for(int i = 0 ; i < m ;i++)
63 {
64 int a,b,c;
65 scanf("%d%d%d",&a,&b,&c);
66 add(a,b,c);
67 }
68 if(!spfa())printf("-1\n");
69 return 0;
70 }
