import java.util.Scanner;

public class Main {

    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        String[] input = scanner.nextLine().split(" ");
        int gate_num = Integer.valueOf(input[1]);

        int gate_min = Integer.MIN_VALUE;
        int gate_max = Integer.MAX_VALUE;

        for(int i = 0; i < gate_num; i++) {
            String[] allow_gate = scanner.nextLine().split(" ");
            int min = Integer.valueOf(allow_gate[0]);
            int max = Integer.valueOf(allow_gate[1]);

            if(min > gate_min) gate_min = min;
            if(max < gate_max) gate_max = max;
        }
        int ans = gate_max - gate_min + 1;
        if (ans < 0) ans = 0;

        System.out.println(ans);
    }
}

/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