import java.util.*;
import java.lang.*;
import java.io.*;

class Main {
    public static void main(String[] args) throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st;

        st =  new StringTokenizer(br.readLine());
        int N = Integer.parseInt(st.nextToken());
        int M = Integer.parseInt(st.nextToken());

        int[][] results = new int[M+1][2];
        
        
        
        for (int i=1; i<M+1; i++) {
            st =  new StringTokenizer(br.readLine());
            results[i][0] = Integer.parseInt(st.nextToken());
            results[i][1] = Integer.parseInt(st.nextToken());
        }


        int X = results[1][0];
        int Y = results[1][1];

        int[] freqX = new int[N+1];
        int absentX = 0;
        int countX = 0;

        ArrayList<String> ans = new ArrayList<>();
        
        for (int i=1; i<M+1; i++) {
            if(X != results[i][0] && X != results[i][1]) {
                freqX[results[i][0]] ++;
                freqX[results[i][1]] ++;
                absentX++;
            }
        }

        if(absentX == 0) {
            countX = N-1;
        } else {
            for (int i=1; i<= N; i++) {
                if(i != X && freqX[i] == absentX) {
                    countX ++;
                }
            }
        }

        int[] freqY = new int[N+1];
        int absentY = 0;
        int countY = 0;

        for (int j=1; j<M+1; j++) {
            if(Y != results[j][0] && Y != results[j][1]) {
                freqY[results[j][0]] ++;
                freqY[results[j][1]] ++;
                absentY ++;
            }
        }

        if(absentY == 0) {
            countY = N-1;
        } else {
            for (int j=1; j<=N; j++) {
                if(j != Y && freqY[j] == absentY) {
                    countY ++;
                }
            }
        }

        boolean is_duple = true;
        for (int i=1; i<=M; i++) {
            if(X!= results[i][0] && Y!= results[i][0] && X!= results[i][1] && Y!= results[i][1]) {
                is_duple = false;
                break;
            }
        }

        // System.out.println(ans);
        int total = countX + countY;
        if(is_duple) total --;
        System.out.println(total);
        
        

    }
}