#include <iostream>
#include <stdio.h>
#include <algorithm>
using namespace std;

struct xxx
{
	int a, b;
}task[10005], s1[10005], s2[10005];

bool cmp1(struct xxx u, struct xxx v)
{
	if (u.a < v.a)
		return true;
	return false;
}
bool cmp2(struct xxx u, struct xxx v)
{
	if (u.b > v.b)
		return true;
	return false;
}

int main()
{
	int n, i, j, k;
	while (scanf_s("%d", &n) && n)
	{
		j = 0, k = 0;
		for (i = 0; i < n; i++)
		{
			scanf_s("%d%d", &task[i].a, &task[i].b);
			if (task[i].a < task[i].b)
			{
				s1[j].a = task[i].a;
				s1[j++].b = task[i].b;
			}
			else
			{
				s2[k].a = task[i].a;
				s2[k++].b = task[i].b;
			}
		}
		sort(s1, s1 + j, cmp1);
		sort(s2, s2 + k, cmp2);

		
		

		int restime = 0, sum = 0;
		for (i = 0; i < j; i++)
		{
			if (i == 0)
			{
				sum += s1[i].a + s1[i].b;
				restime = s1[i].b;
				
				continue;
			}
			if (s1[i].a >= restime)
			{
			
				sum += (s1[i].a - restime) + s1[i].b;
				restime = s1[i].b;
				
			}
			else if (s1[i].a < restime)
			{
				sum += s1[i].b;
				restime = restime - s1[i].a + s1[i].b;
				
			}
		}
		
		
		for (i = 0; i < k; i++)
		{
			if (s2[i].a >= restime)
			{
				sum += (s2[i].a - restime) + s2[i].b;
				restime = s2[i].b;
				
			}
			else
			{
				restime = restime - s2[i].a + s2[i].b;
				sum += s2[i].b;
				
			}
		}
		
		printf("%d\n", sum);
	}
	return 0;
}