题解

#include<bits/stdc++.h>
using namespace std;
bool map1[99999];
int main(){
	int a;
	cin>>a;
	a++;
	int b;
	cin>>b;
	while(b--){
		int x,y;
		cin>>x>>y;
		for(int i=x;i<=y;i++){
			if(map1[i]==0){
				a--;
				map1[i]=1;
			}
		}
	}
	cout<<a;
	return 0;
}