#include <iostream>
#include <cstdio>
#include <vector>
using namespace std ;
int main() {
   int n, m ;
   cin >> n >> m ;
   vector<int> deg(n) ;
   vector<pair<int, int> > e(m) ;
   for (int i=0; i<m; i++) {
      int a, b ;
      cin >> a >> b ;
      a-- ; b-- ;
      if (a > b)
         swap(a, b) ;
      deg[a]++ ;
      deg[b]++ ;
      e[i] = make_pair(a, b) ;
   }
   vector<int> inte(n) ;
   vector<int> intn(n) ;
   int lo = 1 ;
   int hi = n-1 ;
   for (int i=0; i<m; i++) {
      inte[min(deg[e[i].first], deg[e[i].second])]++ ;
      hi = min(hi, max(deg[e[i].first], deg[e[i].second])) ;
   }
   for (int i=0; i<n; i++)
      intn[deg[i]]++ ;
   for (int i=n-1; i>0; i--)
      intn[i-1] += intn[i] ;
   for (int i=n-1; i>0; i--)
      inte[i-1] += inte[i] ;
   int r = 0 ;
   for (int ce=lo; ce<=hi; ce++) {
      int cs = intn[ce] ;
      int clique_edges = inte[ce] ;
// cerr << "At ce " << ce << " cs " << cs << " edges " << clique_edges << endl ;
      if (2 * clique_edges == cs * (cs - 1)) {
         r = 1 ;
         for (int i=0; i<n; i++)
            if ((deg[i] >= ce && deg[i] == cs-1) ||
                (deg[i] < ce && deg[i] == cs))
               r++ ; // can move this into or out of the clique
         break ;
      }
   }
   cout << r << endl ;
}