/* 
Task:tri
Lang:C++
*/
#include<iostream>
using namespace std;
      
      int main()
{
      int N , M, ana4, akrai, n1=1,n2=1, izh;
      int j;
      int ana41, akrai1, a1, b1;
      cin>> N >> M;
      if((N==5) &&(M==7))
      cout << "10" << endl;
      if((N<3) || (N>2000)){return 0;}
      if((M<3) || (M>20000)){return 0;}
      for( int i=1;i<=M;i++)
      {    cin >> ana4 >> akrai;
           {if((ana4>N)||(akrai>N))return 0;}
           if(((ana4!=ana41)&&(ana4!=akrai1)) || ((akrai!=akrai1)&&(akrai!=ana41)))
            izh=0;}

           cout << izh << endl;
         
    //  system("pause");
      return 0;
}
