#yuki_615

n,k=map(int,raw_input().split())
a=map(int,raw_input().split())
a1=sorted(a)
b=[]
for i in xrange(1,n):
 b.append(a1[i]-a1[i-1])
b1=sorted(b,reverse=True)
res=sum(b1)
for i in xrange(k-1):
 res-=b1[i]
print res