#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <math.h>
#include <limits.h>
#define Max(a, b) ((a) > (b) ? (a) : (b))
#define Min(a, b) ((a) > (b) ? (b) : (a))
#define abs(x) ((x) > 0 ? (x) : -(x))
#define MOD 1000000007 //10^9 + 7
#define endl printf("\n")
typedef long long ll;

int
main(int argc, char *argv[])
{
  ll c[100000], d[100000];
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%lld %lld", &c[i], &d[i]);

  ll cost[100000];
  cost[0] = 2 * c[0];
  for (int i = 1; i < n; i++)
    cost[i] = cost[i - 1] + Min(Min(2 * c[i], c[i] + d[i]), 2 * c[i] - c[i - 1] + d[i]);

  printf("%lld\n", cost[n - 1]);

  return 0;
}