/*#include<cstdio>

struct begin_end
{
	long int begin;
	long int end;
};

int main()
{
	long int length, section;
	long int leftTree;
	begin_end *temp;
	scanf("%ld%ld", &length, &section);
	while(true)
	{
		if(length == 0 && section == 0)
		{
			break;
		}
		temp = new begin_end[section];
		leftTree = length + 1;
		for(int i = 0; i < section; i++)
		{
			scanf("%ld%ld", &temp[i].begin, &temp[i].end);
			leftTree -= temp[i].end - temp[i].begin + 1;
		}
		printf("%ld\n", leftTree);
		scanf("%ld%ld", &length, &section);
	}
	return 0;
}*/