#include <iostream>
using namespace std;

int main()
{
	long long int tmpa,tmpb,len,left;
	int n;
	cin>>len>>n;
	while(len && n){
		left = len+1;
		for(int i = 0 ; i  < n ; i++){
			cin>>tmpa>>tmpb;
			left -=(tmpb-tmpa+1);
		}
		cout<<left<<endl;
		cin>>len>>n;
	}
	return 0;
}


不 B4自己不行阿，double和long long int都没分清楚，用double过不了，要用long long int还要去多看下语法了