9分求调

#include<bits/stdc++.h>
using namespace std;
struct grass{
	int h,t,l; 
}a[150000];
bool cmp(grass q,grass w){
	return q.t < w.t;  
}
int main(){
	int n;
	int gress=0;
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>a[i].h>>a[i].t;
		a[i].l = a[i].t - a[i].h + 1;  
	}
	sort(a,a+n,cmp);  
	int last_t = -1; 
	for(int i=0;i<n;i++){ 
		if(a[i].h > last_t){
			gress += a[i].l;
			last_t = a[i].t;  
		}
	}
	cout<<gress;
}