Problem Description
Gug is collecting mushrooms again. There are N farms from which Gug can collect mushrooms. Each farm only has two mushrooms for Gug to collect. To collect the first mushroom from farm i costs Ai dollars, and collecting the second mushroom from farm i costs Bi dollars. The first mushroom must be collected before the second mushroom. Gug needs M mushrooms in total. Find out the minimum amount of money, in dollars, he must pay.
Input
The first line of input will consist of two integers, N and M.
The next N lines of input will contain two integers each, Ai and Bi.
Output
The output should contain one integer, the minimum amount of money Gug needs to pay.
Limits
For all subtasks: 1 ≤ M ≤ 2N, 1 ≤ Ai, Bi ≤ 109.
Subtask 1 (25%): 1 ≤ N ≤ 1000.
Subtask 2 (10%): 1 ≤ N ≤ 200000, Ai = 1.
Subtask 3 (11%): 1 ≤ N ≤ 200000, Ai = Bi.
Subtask 4 (22%): 1 ≤ N ≤ 200000, Ai ≤ Bi.
Subtask 5 (32%): 1 ≤ N ≤ 200000.
Subtask 6 (0%): Sample Testcases.
Sample Input 1
2 3
1 1
1 1
Sample Output 1
3
Sample Input 2
5 3
10 10
5 5
10 10
6 3
25 5
Sample Output 2
14