ln=list(map(int,input().split()))
N=list(map(int,input().split()))
M=[]
rem=[]

for i in range(0,ln[0]):
    n=min(N)
    M.append(n)
    N.remove(n)

for i in range(0,ln[0]-1):
    rem.append(M[i+1]-M[i])

ain=[]
for i in range(0,ln[0]-1):
    n=min(rem)
    ain.append(n)
    rem.remove(n)

ans=0
for i in range(0,ln[0]-ln[1]):
    ans+=ain[i]

print(ans)