#include<iostream>
#include<cstdio>
#include<queue>
#include<vector>
#define ll long long
using namespace std;
int n;
ll a[100005],b[100005];
ll sum[2];
int t;
struct Node{
    ll val;
    int id;
    int g;
    bool operator <(const Node b)const{
        return val<b.val||val==b.val&&g<b.g;
    }
};
priority_queue<Node> q;
int main(){
    freopen("nit.in","r",stdin);
    freopen("nit.out","w",stdout);
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        scanf("%lld %lld",&a[i],&b[i]);
        q.push({a[i],i,1});
    }
    while(!q.empty()){
        sum[t%2]+=q.top().val;
        if(q.top().g==1){
            int i=q.top().id;
            q.pop();
            q.push({b[i],i,2});
        }else
            q.pop();
        t++;
    }
    printf("%lld",sum[0]-sum[1]);
    return 0;
}