Place the Guards

#include <bits/stdc++.h>
using namespace std;
#define PB push_back
#define ZERO (1e-10)
#define INF (1<<29)
#define CL(A,I) (memset(A,I,sizeof(A)))
#define DEB printf("DEB!\n");
#define D(X) cout<<"  "<<#X": "<<X<<endl;
#define EQ(A,B) (A+ZERO>B&&A-ZERO<B)
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef pair<int,int> ii;
typedef vector<ii> vii;
#define IN(n) int n;scanf("%d",&n);
#define FOR(i, m, n) for (int i(m); i < n; i++)
#define REP(i, n) FOR(i, 0, n)
#define F(n) REP(i, n)
#define FF(n) REP(j, n)
#define FT(m, n) FOR(k, m, n)
#define aa first
#define bb second
void ga(int N,int *A){F(N)scanf("%d",A+i);}
#define MX (200)
vi g[MX];
int cn[MX];
bool cc(int n,int x,int &w,int &b){
    if(~cn[n])return cn[n]==x;
    cn[n]=x,++w;
    for(int i:g[n])if(!cc(i,!x,b,w))return 0;
    return 1;
}
bool mc(int N,int&S){
    int a,b;
    S=0,CL(cn,-1);
    F(N)if(!~cn[i]){
        if(!cc(i,0,a=0,b=0))return 0;
        else S+=a&&b?min(a,b):max(a,b);
    }
    return 1;
}
int main(void){
    int N,M,a,b;
    IN(tt)F(tt){
        for(auto&h:g)h.clear();
        scanf("%d%d",&N,&M);
        F(M)scanf("%d%d",&a,&b),g[a].PB(b),g[b].PB(a);
        if(mc(N,a))printf("%d\n",a);
        else printf("-1\n");
    }
    return 0;
}