#include<iostream>

int main()
{
	unsigned long int road;
	int section;
	while(true)
	{
		scanf("%ld %d",&road,&section);
		if(road==0 && section==0)break;
		road++;
		for(int i=0;i<section;i++)
		{
			unsigned long int start,end;
			scanf("%ld %ld",&start,&end);
			unsigned long int distance=end-start; 			                distance++;
			road-=distance;
		}
		printf("%ld\n",road);
	}
	return 0;
}