#include <stdio.h>
typedef struct
{
	int w, b;
} Pers;

int x[1001][16][16];
Pers man[1001];

int max(int i, int w, int b)
{
	int xx;
	xx = x[i - 1][w][b];
	if (i > 0 && w > 0 && xx < x[i - 1][w - 1][b] + man[i].w)
	{
		xx = x[i - 1][w - 1][b] + man[i].w;
	}
	if (i > 0 && b > 0 && xx < x[i - 1][w][b - 1] + man[i].b)
	{
		xx = x[i - 1][w][b - 1] + man[i].b;
	}
	return xx;
}


int main()
{
	int i, N, b, w;

	i = 0;
	while (scanf("%d %d", &man[i].w, &man[i].b) != -1) i++;

	N = i;

	memset(x, 0, sizeof(x));
	x[0][0][0] = 0;
	x[0][1][0] = man[0].w;
	x[0][0][1] = man[0].b;
	
	for (b = 0; b < 16; b++)
	{
		for (w = 0; w < 16; w++)
		{
			for (i = b + w - 1; i < N; i++)
			{
				if (b + w + i < 2)
				{
					continue;
				}
				x[i][w][b] = max(i, w, b);
			}
		}
	}
	printf("%d\n", x[N - 1][15][15]);
	return 0;
}