C++ :

#include <bits/stdc++.h>
using namespace std;

long long a[300000];//存放两张牌和差值

int main(){
	long long n,i,j,x,y,k,s_x,s_y,s;
	cin>>n;
	//统计上面的牌比下面的大的有多少
	//上面的比下面的小不会有人拿
	k = 0; 
	s = 0;
	for(i = 0;i < n;i++){
		cin>>x>>y;
		if(x >= y){
			a[k] = x;
			a[k + 1] = y;
			k = k + 2;
			s = s + x + y;	
		}
	}
	
	//数组排序
	sort(a,a+k);
	
	
	//初始化得分
	s_x = 0;
	s_y = 0;
	for(i = k - 1;i >= 0;i = i - 2){
		s_x = s_x + a[i];
	} 
	s_y = s - s_x;
	cout<<s_x - s_y<<endl;
}