#include<bits/stdc++.h>
using namespace std;
#define int long long
int n;
int ans[2];
typedef pair<int,int> PII;
priority_queue<PII,vector<PII>,less<PII> >q;
signed main(){
    freopen("nit.in","r",stdin);
    freopen("nit.out","w",stdout);
    
    cin>>n;
    for(int i=1;i<=n;i++){
        int a,b;
        cin>>a>>b;
        q.push({a,-b});
    }
    bool flag=0;
    while(1){
        int val1=q.top().first;
        int val2=q.top().second;
//        cout<<val1<<" "<<val2<<"\n";
        if(val1==0) break;
        val2=-val2;
        q.pop();
        q.push({val2,0});
        ans[flag]+=val1;
//        cout<<flag<<":"<<val1<<"\n";
        flag=!flag;
    }
    cout<<ans[0]-ans[1];
    return 0;
} 
/*
4
3 2
1 3
2 5
4 1

4
101 99
100 2
2 1
1 2

*/