#include<bits/stdc++.h> 
using namespace std;
long long n,a[100005],b[100005],np,p,pp,ppp,pppp,s1,s2;
priority_queue<pair<pair<long long,long long>,pair<long long,long long> > >q;
int main(){
    freopen("nit.in","r",stdin);
    freopen("nit.out","w",stdout);
    ios::sync_with_stdio(false);
    cin>>n,np=n+n;
    for(int i=1;i<=n;i++) cin>>a[i]>>b[i],q.push({{a[i],-b[i]},{i,1}});
    while(np--){
        p=q.top().first.first,pp=-q.top().first.second,ppp=q.top().second.first;
        pppp=q.top().second.second,q.pop();
        if(np%2){
            s1+=p;
            if(pppp==1) q.push({{b[ppp],0},{pp,2}});
        }else{
            s2+=p;
            if(pppp==1) q.push({{b[ppp],0},{pp,2}});
        }
    }
    cout<<s1-s2;
    return 0;
}