#include<iostream>
using namespace std;
int main()
{
	int num, length;
	cin >> length >> num;
	int *arr1 = new int[length]();
	
	int(*arr)[2] = new int[num][2];
	for (int i = 0; i < num; i++)
	{
		cin >> arr[i][0];
		cin >> arr[i][1];
		for (int j = arr[i][0]; j <= arr[i][1]; j++)
		{
			arr1[j - 1] = 1;//做标记
		}//但除了普通数组这种方法外，是否有其他更简便的方式？比如vector
	}
	int counter = 0;
	for (int i = 0; i < length; i++)
	{
		if (arr1[i] == 0)
		{
			counter++;
		}
	}
	cout << counter+1 << endl;
	delete arr1;
	delete[] arr;
	return 0;
}