#!/usr/bin/python2
# -*- coding: utf-8 -*-
# †
from itertools import tee
# s -> (s0,s1), (s1,s2), (s2,s3), ...
def pairwise(iterable):
    a, b = tee(iterable)
    next(b, None)
    return zip(a, b)


N, K = map(int, raw_input().split())
a = map(int, raw_input().split())
a.sort()
difs = [q-p for p, q in pairwise(a)]
difs.sort()
res = a[-1] - a[0]
if K > 1:
    res -= sum(difs[-K+1:])
print res