import java.util.*;

class Main{
    public static void main(String[] args) {
        Scanner stdIn = new Scanner(System.in);
        int n = stdIn.nextInt();
        int m = stdIn.nextInt();
        int L[] = new int [m];
        int R[] = new int [m];
        int maxL = 1; int minR = n;
        for(int i = 0; i < m; i++){
            L[i] = stdIn.nextInt();
            R[i] = stdIn.nextInt();
            if(maxL < L[i]) maxL = L[i];
            if(minR > R[i]) minR = R[i];
        }

        System.out.println(minR-maxL+1 >= 0 ? minR-maxL+1 : 0 );
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz