N,K=map(int,input().split())
A=list(map(int,input().split()))
A.sort()

MAX=A[-1]-A[0]

ku=K-1

B=[A[i]-A[i-1] for i in range(1,N)]

B.sort(reverse=True)

for i in range(ku):
    MAX-=B[i]

print(MAX)