"""

https://yukicoder.me/problems/no/615


https://atcoder.jp/contests/abc414/submissions/67537669
と同じ

"""

import sys
from sys import stdin

N,M = map(int,input().split())

X = list(map(int,input().split()))
X.sort()

ans = X[-1] - X[0]

D = [ X[i+1]-X[i] for i in range(N-1) ]
D.sort()

for i in range(M-1):
    ans -= D[-1-i]

print (ans)