1 #include<stdio.h>
2 #define MAXN 1005
3 #include<iostream>
4 #include<algorithm>
5 #define inf 10000000
6 using namespace std;
7 int _m[MAXN][MAXN];
8 int low_cost[MAXN];
9 int pre[MAXN];
10 unsigned prime(int n);
11 int DFS(int i,int sum,int p);
12 bool mark[MAXN];
13 int main()
14 {
15 //freopen("acm.acm","r",stdin);
16 int p;
17 int edge;
18 unsigned tem;
19 int i;
20 int j;
21 int u;
22 int v;
23 while(cin>>p>>edge)
24 {
25 memset(mark,false,sizeof(mark));
26 for(i = 0; i < p; ++ i)
27 {
28 for(j = 0; j < p; ++ j)
29 _m[i][j] = inf;
30 }
31 for(i = 0; i < edge; ++ i)
32 {
33 cin>>u>>v;
34 -- u;
35 -- v;
36 cin>>tem;
37 if(_m[u][v] == inf)
38 {
39 _m[u][v] = tem;
40 _m[u][v] *= -1;
41 _m[v][u] = _m[u][v];
42 }
43 else
44 if(tem > _m[u][v]*(-1))
45 {
46 _m[u][v] = tem;
47 _m[u][v] *= -1;
48 _m[v][u] = _m[u][v];
49 }
50 }
51 mark[0] = true;
52 tem = -prime(p);
53 if(DFS(0,1,p) == p)
54 cout<<tem<<endl;
55 else
56 cout<<-1<<endl;
57 }
58 }
59 int DFS(int i,int sum,int n)
60 {
61 int j;
62 for(j = 0; j < n; ++ j)
63 {
64 if(i != j && _m[i][j] != inf && !mark[j])
65 {
66 mark[j] = true;
67 sum = DFS(j,sum+1,n);
68 }
69 }
70 return sum;
71 }
72 unsigned prime(int n)
73 {
74 int i;
75 int j;
76 int k;
77 unsigned sum = 0;
78 int min;
79 for(i = 1; i < n; ++ i)
80 {
81 low_cost[i] = _m[0][i];
82 pre[i] = 0;
83 }
84 for(i = 1; i < n; ++ i)
85 {
86 min = inf;
87 for(j = 1; j < n; ++ j)
88 {
89 if(low_cost[j]&&low_cost[j] < min)
90 {
91 k = j;
92 min = low_cost[j];
93 }
94 }
95 sum += low_cost[k];
96 low_cost[k] = 0;
97 for(j = 1; j < n; ++ j)
98 {
99 if(_m[k][j] < low_cost[j] && low_cost[j])
100 {
101 low_cost[j] = _m[k][j];
102 pre[j] = k;
103 }
104 }
105 }
106 return sum;
107 }
