#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int n;
struct node{
	ll x,y;
	bool operator < (const node &t) const {
		if(x==t.x) return y>t.y;
		return x<t.x;
	}
};
priority_queue<node> q;
ll ans;
int main(){
	freopen("nit.in","r",stdin);
	freopen("nit.out","w",stdout);
    cin>>n;
    for(int i=1;i<=n;i++){
    	ll a,b;
    	cin>>a>>b;
    	q.push({a,b});
    }
    for(int i=1;i<=n*2;i++){
    	node t=q.top();
    	q.pop();
    	if(i&1){
    		ans+=t.x; 
		}
		else ans-=t.x;
		if(t.y!=-1){
			q.push({t.y,-1});
		}
	}
	cout<<ans;
    return 0;
}