#include <bits/stdc++.h>
using namespace std;

int main() {
	priority_queue<int> pQ;
	int ans = 0;
	int n;
	scanf("%d", &n);
	for (int i = 0; i < n; ++i) {
		int c, a;
		scanf("%d %d", &c, &a);
		ans += c;
		pQ.push(c - a);
		if (i%2 == 0) {
			ans += -pQ.top();
			pQ.pop();
		}
	}
	printf ("%d\n", ans);
	return 0;	
}