URI Online Judge | 2643


By ACM-ICPC World Finals 2017 US United States

Timelimit: 2

Pixels in a digital picture can be represented with three integers in the range 0 to 255 that indicate the intensity of the red, green, and blue colors. To compress an image or to create an artistic effect, many photo-editing tools include a “posterize” operation which works as follows. Each color channel is examined separately; this problem focuses only on the red channel. Rather than allow all integers from 0 to 255 for the red channel, a posterized image allows at most k integers from this range. Each pixel’s original red intensity is replaced with the nearest of the allowed integers. The photo-editing tool selects a set of k integers that minimizes the sum of the squared errors introduced across all pixels in the original image. If there are n pixels that have original red values r1 , . . . , rn , and k allowed integers v1 , . . . , vk , the sum of squared errors is defined as

Your task is to compute the minimum achievable sum of squared errors, given parameter k and a description of the red intensities of an image’s pixels.


The first line of the input contains two integers d (1 ≤ d ≤ 256), the number of distinct red values that occurin the original image, and k (1 ≤ kd), the number of distinct red values allowed in the posterized image. The remaining d lines indicate the number of pixels of the image having various red values. Each such line contains two integers r (0 ≤ r ≤ 255) and p (1 ≤ p ≤ 226 ), where r is a red intensity value and p is the number of pixels having red intensity r. Those d lines are given in increasing order of red value.


Display the sum of the squared errors for an optimally chosen set of k allowed integer values.

Input Samples Output Samples

2 1
50 20000
150 10000


2 2
50 20000
150 10000


4 2
0 30000
25 30000
50 30000
255 30000