1 #include<stdio.h>
2 #include<string.h>
3 #define MAXN 100
4 #define INF 0x3fffffff
5 int n,m,g[MAXN][MAXN],indegree[MAXN],ve[MAXN];
6 void read();
7 int topsort();
8 int main(){
9 int cost;
10 read();
11 cost = topsort();
12 if(cost==-1) printf("Impossible\n");
13 else printf("%d",cost);
14 return 0;
15 }
16 void read(){
17 scanf("%d %d",&n,&m);
18 int i,j,v1,v2,lastime;
19 for(i=0;i<n;i++)
20 for(j=0;j<n;j++)
21 g[i][j] = INF;
22 for(i=0;i<n;i++) indegree[i]=0;
23 for(i=0;i<m;i++){
24 scanf("%d %d %d",&v1,&v2,&lastime);
25 g[v1][v2] = lastime;
26 indegree[v2]++;
27 }
28 }
29 int topsort(){
30 int i,j,count=0,seq[MAXN];
31 int cost,time,point;
32 for(i=0;i<n;i++) ve[i] = 0;
33 j=0;
34 for(i=0;i<n;i++){
35 if(indegree[i]==0)seq[j++] = i;
36 }
37 count = j;
38 j=0;
39 while(count>j){
40 point = seq[j];
41 j++;
42 for(i=0;i<n;i++){
43 if(g[point][i]!=INF&&i!=point){
44 indegree[i]--;
45 if(ve[i]<ve[point]+g[point][i])
46 ve[i] = ve[point]+g[point][i];
47 if(indegree[i]==0){
48 seq[count++] = i;
49 }
50 }
51 }
52
53 }
54 if(count==n){
55 cost = 0;
56 for(i=0;i<n;i++){
57 if(cost<ve[i]) cost = ve[i];
58 }
59 return cost;
60 }
61 else return -1;
62
63 }
