1 //hdu1853
2 #include<stdio.h>
3 #include<string.h>
4 #define INF 99999999
5 int map[103][103],pr[103],pl[103],visr[103],visl[103],slack[103],match[103];
6 int n,m;
7 int dfs(int u)
8 {
9 int i,j,val;
10
11 visl[u]=1;
12 for(i=1;i<=n;i++)
13 {
14 if(!visr[i])
15 {
16 val=pr[i]+pl[u]-map[u][i];
17 if(val==0)
18 {
19 visr[i]=1;
20 if(match[i]==-1||dfs(match[i]))
21 {
22 match[i]=u;
23 return 1;
24 }
25 }
26 if(val>0&&slack[i]>val)
27 slack[i]=val;
28 }
29 }
30 return 0;
31 }
32 void km()
33 {
34 int i,j,res=0,d;
35 for(i=0;i<=n;i++)
36 pl[i]=INF;
37 memset(pr,0,sizeof(pr));
38 memset(match,-1,sizeof(match));
39 for(i=1;i<=n;i++)
40 {
41 for(j=1;j<=n;j++)
42 slack[j]=INF;
43 while(1)
44 {
45 memset(visr,0,sizeof(visr));
46 memset(visl,0,sizeof(visl));
47 if(dfs(i))
48 break;
49 d=INF;
50 for(j=1;j<=n;j++)
51 {
52 if(!visr[j]&&d>slack[j])
53 d=slack[j];
54 }
55 for(j=1;j<=n;j++)
56 {
57 if(visr[j])
58 pr[j]+=d;
59 if(visl[j])
60 pl[j]-=d;
61 }
62 }
63 }
64 }
65 int main()
66 {
67 int i,j;
68 while(scanf("%d%d",&n,&m)!=EOF)
69 {
70 for(i=0;i<=n;i++)
71 for(j=0;j<=n;j++)
72 map[i][j]=-INF;
73
74 for(i=0;i<m;i++)
75 {
76 int x,y,z;
77 scanf("%d%d%d",&x,&y,&z);
78 if(map[x][y]<-z)
79 {
80 map[x][y]=-z;
81 }
82 }
83 /*for(i=1;i<=n;i++)
84 {
85 for(j=1;j<=n;j++)
86 printf("%d ",map[i][j]);
87 printf("\n");
88 }*/
89 km();
90 int flag=1;
91 int res=0;
92 for(i=1;i<=n;i++)
93 {
94 if(map[match[i]][i]==-INF)
95 {flag=0;break;}
96 else res+=map[match[i]][i];
97 }
98 if(!flag)printf("-1\n");
99 else
100 printf("%d\n",-res);
101 }
102 }
