P1496

#include<bits/stdc++.h>
using namespace std;
int ans[200000001] ;
int main(){
	long long int a,b,s=0,n,minn=1919810,maxx=-1919810;
	cin>>n;
	for(long long int i=1;i<=n;i++){
		cin>>a>>b;
		minn=min(a,minn);
		maxx=max(b,maxx);
		for(long long int j=a;j<b;j++){
			ans[j]=1;
		}
	}
	for(long long int i=minn;i<=maxx-1;i++){
		if(ans[i])s++;
	}
	printf("%ld",s);
	return 0;
} 

一点RE