POJ 2665 Trees

额，如果不认真看题还以为是线段树呢。。

看到It is confirmed that these sections do not overlap with each other这句话就知道这题有多水了。。

#include <cstdio>
using namespace std;
int main(){
	int r,n,res,a,b;
	while(scanf("%d%d",&r,&n)){
		if(!r&&!n)break;
		res=r+1;
		for(int i=0;i<n;i++){
			scanf("%d%d",&a,&b);
			res-=b-a+1;
		}
		printf("%d\n",res);		
	}
	return 0;
}