#include<iostream>
#include<cstring>
#include<map>
#include<stack>
#include<algorithm>
#define MAX 10000000;
using namespace std;
 
 int main(){
 
 
	long long int test_case,w=1;
	cin>>test_case;
	  	int winner[10],infcount=0;
	while(w<=test_case){
 
		long long int n,d; // process (1 to n), dependencies 
		cin>>n>>d;
		bool matrix[n+1][n+1];
		memset(matrix,0,sizeof(matrix));
		long long int i;
 
		for(i=1;i<=d;i++){
			long long int process,dependency;
			cin>>process>>dependency;
			matrix[process][dependency] = 1;
		}
		map<long long int,long long int> degree;
		for(i=1;i<=n;i++){
			long long int count = 0;
			for(long long int j=1;j<=n;j++){
				if(matrix[j][i]==1)
					count++;
			}
			degree[i] = count;
		}
		long long int result = 0;
		while(!degree.empty()){
			map<long long int,long long int>::iterator it = degree.begin() , end = degree.end() , temp;
			bool flag = 0;
			stack< map<long long int,long long int>::iterator > st;
			while(it!=end){
				if(it->second == 0){
					st.push(it);
					flag = 1;
				}
				it++;
			}
			while(!st.empty()){
				temp = st.top();
				st.pop();
				long long int index = temp->first;
				// cout<<index<<" ";
				degree.erase(temp);
				for(long long int j = 1;j<=n;j++){
					if(matrix[index][j]==1){
						matrix[index][j] = 0;
						degree[j]--;
					}
				}
			}
			if(flag==0)
				break;
			result++;
		}
		if(!degree.empty()){
			infcount++;
			winner[w]=MAX;
 
	    	}
		else{
			winner[w]=result;
 
		    }
		w++;
	}
	  int min=MAX;int flag=0,team;
 
	if(infcount==test_case)
		 cout<<"0";
		 else{
 
				   for(int i=1;i<=test_case;i++){
				   	      if(winner[i]<min){
				   	      	  min=winner[i];
				   	      	    team=i;
							 }
				     } 	
 
				    for(int i=1;i<=test_case;i++)
				     if(winner[i]==min)
				      flag++;
 
				      if(flag>=2)
				        cout<<"0";
				      else
				        cout<<team;
		    }
 
 
	return 0;
}
 

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6
40 50
37 1
15 3
5 4
18 5
23 6
26 7
20 8
37 9
21 10
34 11
32 12
24 13
1 14
12 15
35 16
37 17
15 18
12 19
32 20
24 21
14 22
2 23
1 24
30 25
31 26
26 27
23 28
19 29
32 30
32 31
2 32
31 33
20 34
37 35
10 36
2 37
15 38
29 39
29 40
8 10
24 2
13 22
11 26
21 19
33 37
31 8
32 21
9 8
34 40
17 39
12 24
11 1
4 2
8 3
11 4
4 5
10 6
11 7
11 8
4 9
7 10
7 12
1 4
3 9
5 6
1 7
5 2
7 4
9 2
1 9
4 8
8 6
4 10
6 11
4 6
4 6
2 1
3 2
3 4
4 1
2 4
1 3
3 6
1 2
3 1
3 2
2 1
1 3
1 2
6 30
1 2
1 3
1 4
1 5
1 6
2 1
2 3
2 4
2 5
2 6
3 2
3 1
3 4
3 5
3 6
4 2
4 3
4 1
4 5
4 6
5 2
5 3
5 4
5 1
5 6
6 2
6 3
6 4
6 5
6 1
4 2
1 2
2 1
5 8
1 2
1 3
1 4
1 5
5 4
2 5
2 1
3 5