1 /**************************************************
 2  * Author     : xiaohao Z
 3  * Blog     : http://www.cnblogs.com/shu-xiaohao/
 4  * Last modified : 2014-01-28 08:40
 5  * Filename     : uva_11080.cpp
 6  * Description     : 二分图染色
 7  * ************************************************/
 8
 9 #include <iostream>
10 #include <cstdio>
11 #include <cstring>
12 #include <cstdlib>
13 #include <cmath>
14 #include <algorithm>
15 #include <queue>
16 #include <stack>
17 #include <vector>
18 #include <set>
19 #include <map>
20 #define MP(a, b) make_pair(a, b)
21 #define PB(a) push_back(a)
22
23 using namespace std;
24 typedef long long ll;
25 typedef pair<int, int> pii;
26 typedef pair<unsigned int,unsigned int> puu;
27 typedef pair<int, double> pid;
28 typedef pair<ll, int> pli;
29 typedef pair<int, ll> pil;
30
31 const int INF = 0x3f3f3f3f;
32 const double eps = 1E-6;
33 const int LEN = 501;
34 int n, m, vis[LEN];
35 vector<int> Map[LEN];
36
37 bool dfs(int v, int col){
38     vis[v] = col;
39     for(int i=0; i<Map[v].size(); i++){
40         if(vis[Map[v][i]] == 0) {if(!dfs(Map[v][i], -col))return false;}
41         else if(vis[Map[v][i]] == col) return false;
42     }
43     return true;
44 }
45
46 int main()
47 {
48 //    freopen("in.txt", "r", stdin);
49
50     int T, a, b;
51     scanf("%d", &T);
52     while(T--){
53         scanf("%d%d", &n, &m);
54         for(int i=0; i<LEN; i++)Map[i].clear();
55         memset(vis, 0, sizeof vis);
56         for(int i=0; i<m; i++){
57             scanf("%d%d", &a, &b);
58             Map[a].PB(b);
59             Map[b].PB(a);
60         }
61         int ans = 0, col = 0;
62         for(int i=0; i<n; i++)
63             if(vis[i] == 0){
64                 if(dfs(i, ++col)==false){
65                     ans = -1;
66                     break;
67                 }
68                 int cnt = 0, rcnt = 0;
69                 for(int i=0; i<n; i++){
70                     if(vis[i]==col)cnt++;
71                     if(vis[i]==-col)rcnt++;
72                 }
73                 ans += max(1, min(cnt, rcnt));
74             }
75         if(ans<0)printf("-1\n");
76         else printf("%d\n", ans);
77     }
78     return 0;
79 }