SAWMILL  Two Swamills
There are old trees planted along a road that goes from the top of a hill to its bottom. Local government decided to cut them down. In order not to waste wood each tree should be transported to a sawmill.
Trees can be transported only in one direction: downwards. There is a sawmill at the lower end of the road. Two additional sawmills can be built along the road. You have to decide where to build them, as to minimize the cost of transportation. The transportation costs one cent per meter, per kilogram of wood.
Input
The first line of the input contains one integer  the number of trees (). The trees are numbered , starting from the top of the hill and going downwards. Each of the following lines contains two positive integers separated by single space. Line contains:  weight (in kilograms) of the th tree and  distance (in meters) between trees number and , , . The last of these numbers, , is the distance from the tree number to the lower end of the road. It is guaranteed that the total cost of transporting all trees to the sawmill at the end of the road is less than cents.
Output
The first and only line of output should contain one integer: the minimum cost of transportation.
Example
Input:9 1 2 2 1 3 3 1 1 3 2 1 6 2 1 1 2 1 1
Output:26
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vaibhav2303:
20181105 11:53:24
Constraints? 

sbansalcs:
20160902 19:38:09
Nice Problem. 

owt:
20140215 13:25:05
guys who have solved it help me please. Could you suggest any hint or algorithm, because I am so desperate in solving this :D Last edit: 20140319 13:25:24 
Added by:  acheron 
Date:  20140104 
Time limit:  0.300s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ASM64 
Resource:  CEOI 2004 