n,m=gets.split.map{|e| e.to_i}
x=gets.split.map{|e| e.to_i}.sort
y=[]
if n==1
	puts 0
else
(0..x.size-2).each{|i|
	y<<(x[i+1]-x[i])
}
y.sort!
ans=0
(n-m).times{|i|
	ans+=y[i]
}
puts ans
end