#define F first
#define S second
#define rep(i,a,b) for(int i=a;!(a==b&&i!=b)&&((i<=b&&b>=a)||(i>=b&&a>=b));i+=(a<=b?1:-1))
#define pb push_back
#define Fbitl __builtin_ffs
#define bit1 __builtin_popcount
#include <iostream>
#include <math.h>
#include <algorithm>
#include <string.h>
#include <vector>
#include <queue>
#include <map>
#include <unordered_map>

using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<string, string> pss;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vii;
typedef vector<ll> vl;
typedef vector<vl> vvl;

int main() {
	int n,a,b ;
	ll res = 0;
	cin >> n;
	priority_queue <pair<int,pii>> x ;
	for ( int i = 0 ; i < n ; i++ ) { 
		cin >> a >> b;
		res += a ;
		x.push({b-a,{a,b}});
	}
	for ( int i = 0 ; i < n/2 ; i++ ) {
		res += x.top().F ;
		x.pop();
	}
	cout << res ;
	return 0;
}